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Problem Tracker for Mechanics ReView Summer 2013
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DateIssuePosted ByResolved By<-- Mouseover to read comments.
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4/29/2013https://www.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/Unit_1/Newtons_Second_Law/3This is just an example. Note the "3" at the end that lets it link to the 3rd file in this sequence - you will need to add that by hand.cfred@mit.educfred@mit.edu
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5/17/2013https://www.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/HWK_6/Applying_SIM_to_Problems_in_Planar_Dynamics_Homework/14There are four true/false questions with one free response question, but there are ten submissions.brian.j.yue@gmail.comtoo late to change -alwinaHow many submissions are there supposed to be? Also, added correct link. -Aaron
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5/23/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/Unit_13/Keplerian_Orbit_Model/20asked in quiz 12brian.j.yue@gmail.comcfred@mit.eduRemoved. Quiz question kept.
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5/31/2013https://staging.mitx.mit.edu/courses/MITx/8.MReV/2013_Summer/courseware/Testing/Test_Problem/5The note in part one gives away the answers. Was this intentional?brian.j.yue@gmail.comdisappeared
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6/1/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/Unit_1/Net_Force_and_Vector_Addition/9The text and diagrams for several of the sections run off the page to the rightjeff@college-prep.orgPotential solution: split up the graphics. They may be forcing the table wider.
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6/3/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/HWK_11/Angular_Momentum_Homework/106/3/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/Unit_6/Multiple_Models_Constraints_and_Two-Dimentional_Projectile_Motion/9Uh... not sure what happened here...
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6/9/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/Unit_4/Graphing_Motion_Acceleration_vs._Deceleration/6apparently the diagrams of example 1 and 2 are not visible or too small when using safary or chrome browsers and on ipadsmixson1977@gmail.comcfred@mit.eduNo known fix. May need to recreate tables without nesting and hide/show behavior.
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6/22/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/Introduction/Introduction_to_the_course/3Missing andgular impulse in agent of change lineanaliabcfred@mit.eduWill fix for next run.
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6/23/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/Unit_3/Point_Particle_System_and_EnvironmentInternal_and_External_Forces/apparently the diagrams of example 1 and 2 are not visible or too small when using safary or chrome browsers and on ipadsclaudia.fracchiolla@gmail.comcfred@mit.eduNo known fix. May need to recreate tables without nesting and hide/show behavior.
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7/3/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/Unit_9/Statics_and_Free_Choice_of_Axis/2The static friction coefficient for the floor in Part A calculated at the end of Part B should be 0.18, and the static friction coefficient forthe wall in Part B should be 1.17. I realize these are small differences from what is on the screen, but a novice student may get confused. Also, in the Answer section below part B, should the ??? = "arm"?pgeschke7@comcast.netcfred@mit.edufixed ??? -> arm. Not sure about the other two; too late at night to think about it right now. Will reexamine later.
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7/8/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/Unit_8/Mechanical_Energy_and_Work/ (Advanced Material) Model: First Law of Thermodynamics - Concept Question - Statement 3 "The sum of the heat energy added and the amount of work added is independent of the path" is not correct but the correct answer is given as - " The sum of the heat and the work is equal to the change in the Energy, and that is independent from the path taken" Need to change statement 3 in the question.george@andronov.comcfred@mit.eduWill refer this to Dr. Pritchard for review.
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https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/HWK_10/Describing_Rotational_and_Translational_Motion_Homework/15I found the description of 'slipping' a bit confusing until I read part b. It's not immediately clear that it is a problem involving a car wheel under various conditions. A more complete description would be useful.jeff@college-prep.orgLink seems to point to wrong problem.
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https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/Unit_8/Energy_Bar_Diagrams/3The second question comes beforte the discussion of the material; also, as pointed out by a student, the shape of the curve is not known at the point in question and so there is no way to answer logicallyspconverse@waketech.eduThe answer seems fairly logical to me... --Colin
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7/28/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/HWK_8/Mechanical_Energy_and_Work_Homework/11In block on wedge 3 (page 11), it might be better to put the answers in a table so it is easier to see the change that goes with each property.jeff@college-prep.organaliab@mit.edufor next course
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7/30/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/Unit_12/Kinematics_of_Simple_Harmonic_Motion/br {mso-data-placement:same-cell;}The use of the word diplacement rather than position should be considered in a future update of the course? For example on page 2 but it should not be a change for all occurances of position. Also I cannot find in this section any formal definition of the term "amplitude".george@andronov.comwhat page? Page 2 - Simple Harmonic Motion: Matching Initial Position and Velocity
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7/3/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/Unit_12/Damped_and_Driven_Harmonic_Oscillations/First page right at the bottom - "If the natural frequency of oscillations is greater than the driving frequency, the solution will be in phase with the driving force. If, however, the natural frequency is less than the driving frequency the prefactor will turn negative and the oscillations will go 180° out of phase with the driving" - I do not think this is correct. As one goes away from the resonant frequency the phase shifts towards zero and 180° dependent on whether the driver frequency is decreasing or increasing nut it is a "gradual" process not "instantaneous" as implied by the passage I have quoted above?george@andronov.com
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8/1/2013The cross-product problems throw an odd error when you give them "x" rather than "+x".cfred@mit.edu(I'm on it - Colin)
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8/3/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/discussion/forum/MReV_Summer2013_Angular_Momentum_of_1/threads/51fc54ef40262d1200000035Student has commented on some errors and given a suggestion.george@andronov.com
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8/3/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/discussion/forum/MReV_Summer2013_Gravity_and_Orbits/threads/51fc2e74b974ca0e00000022Student has commented on a error.george@andronov.com
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8/4/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/HWK_9/Torque_and_Rotation_about_a_Fixed_Axis_Homework/2Torque direction problem. It might be clearer if the centre of mass was stated to be at the origin?george@andronov.comcfred@mit.eduNot actually necessary - direction is given from C of M.
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8/4/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/Unit_9/Choosing_an_Axis_of_Rotation_and_Describing_the_Direction_of_Rotation/3A lot of students commented in the discussion that the diagram doesn't follow the right-hand rule, which is think is precipitated by two problems: 1. the purpose of the illustration is not clear (to show vector notation; the students think it is an illustration of the right-hand rule), and 2. the drawing is labelled "opens toward viewer" which a lot of students are taking as the door being in the process of opening, and taking this as an illustration of positive angular velocity. I recommend adding a title to the illustration, and taking off the label; I think the hinges make the direction of motion clear enough.msittig@gmail.com
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8/8/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/Unit_10/Rotational_Energy/7Video cannot be seen or downloaded.From one student "I get the same access denied error as well when I try to download it. I get this same error in Chrome and Firefox. In IE I cant access any edx content, the message 'ERROR: Unable to load Sequence: Object expected' always appears."george@andronov.comHrm. Wish I knew what happened to that video. I'll see what I can do about this.
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8/10/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/discussion/forum/MReV_Summer2013_compare_position/threads/5205537e43c9eb0a0000001aStudent fwizbang thinks the grader is in error. Please will you check as I think he has a point. Looking back also got this question marked wrong with final value os xA = +4.7 and xB = -4.4566 having given an answer A.george@andronov.comCreativeAhaan@gmail.comI believe there is no error with this. I got it correct with no discomfort.SignoriC also seems to have the grader error (if s/he has provided the accurate value as given on the forum)
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8/15/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/Unit_14/One_Step_Problems_and_Simultaneous_Models/3Checkpoint 1: Spring and Two Masses - two possible responses in Part 4 are the same.george@andronov.comalwina@mit.edufixed
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8/16/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/HWK_14/Review_Homework/1The video "Tne Physics of Unicycling" seems not to be available on a PC running Firefox (mine) and anothe rstudent has also reported such a problem and I have asked for more details. I have provided the temporay link in my post as http://video.mit.edu/watch/the-physics-of-unicycling-10929/george@andronov.com
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8/16/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/Quiz_11/Quiz_11/Question 8 (Center of Mass, Review) does not mention that you can use "v" or "d" in your answer. The wording seems to imply only m1, m2, t1 and t0. Perhaps d and v should be made explicit options (as both are necessary).chrisbecke@yahoo.comalwina@mit.edufixed
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8/17/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/HWK_10/Describing_Rotational_and_Translational_Motion_Homework/4I would class this as an urgent issue as the deadline for this homework is very close. Problem no longer visible. If it has been removed then a note to that effect should be posted in its place and also there should be a note under "Course Info".george@andronov.comcfred@mit.eduFixed (before deadline).
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8/17/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/Unit_11/Angular_Momentum_of_a_Rigid_Body_Rotating_About_a_Fixed_Axis/8See Discussion below the text for details concerning a typo in the posted solution.geddesphysics@gmail.com
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8/17/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/discussion/forum/MReV_Summer2013_String_and_Post_Configurations/threads/520f72fd6d37171200000007Urgent: The grader for Part 2 is not working correctly (and is accepting incorrect answers). I entered the answer for Part 3 in Part 2 and the grader marked it as correct.asishkm@gmail.comresponded to below
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8/17/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/HWK_14/Review_Homework/22Collision of two spheres that rolled down the inclined planes - Please translte the second sentence "They are fixed in place a frictionless plane." I assume that since the masses of the inclined planes are not given they bolted to the surface?george@andronov.comcfred@mit.eduYes, bolted to the surface. I'll try to improve the wording.
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8/17/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/HWK_14/Review_Homework/21Horizontal meter stick with almost no strings attached - might it be better to warn the students that the answer given in the list are approximate, rounded to 1 dp etc? If this was done then the answer "g" would have to be changed to "1.0 g"? Perhaps chamging the wording in the last line to "What is the approximate acceleration of the midpoint of the meter stick . . . . . " would do it?george@andronov.comcfred@mit.eduThe answer is actually correct as given.
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8/17/2013https://courses.edx.org/static/content-mit-mrev~2013_Summer/handouts/MAPSeqns_updated.pdfA student pointed this out in the discussion forum: https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/discussion/forum/mrev_Summer2013_Suggestions/threads/520f9f69aaefde0a0000000f On page 1 of the MAPS Equation Sheet for 8.011, under the "*Harmonic Motion" section, the far right omega on the line entitled "Differential Law of Change" should be squared.mixson1977@gmail.com
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8/18/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/HWK_11/Angular_Momentum_Homework/15String and Post Configurations - an number of students have suggested that there is a problem with the grader. Here is a thread worth looking at? https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/discussion/forum/undefined/threads/520b7e9b796cba1600000014 and another https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/discussion/forum/undefined/threads/52112964ed202f0e00000019george@andronov.comWill consider. --Colin
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8/18/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/Unit_11/Applications_of_the_Angular_Momentum_and_External_Torque_Model/1Illustrative Example: Down The Ramp / Mathematical Representation - right at the end the last two occurances of "I" should be I subscript cm.george@andronov.comcfred@mit.edufixed
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https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/Unit_11/Angular_Momentum_of_a_Rigid_Body_Rotating_About_a_Fixed_Axis/3In the proof for the "1. Rotation about an axis passing through the Center of Mass", in the expression for L^{2}_{S,z}, there should not be a 'negative' sign, since the L_z component is positive which is in fact confirmed when adding the two L_z components in the next step.asishkm@gmail.com
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8/19/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/HWK_13/Orbits_Homework/5The fourth sentence should read "When the satellite reaches the aphelion of that orbit, . . ."mixson1977@gmail.comcfred@mit.edufixed
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8/20/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/HWK_14/Review_Homework/6Ranking the heat in inelastic collision - "Scenario B. Particle 2m chases particle m and collides with it from behind." should be 3m not m.george@andronov.comcfred@mit.edufixed
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8/21/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/discussion/forum/MReV_Summer2013_BK117/threads/51fec7de07884a1600000017I did not see you (Colin) had replied to the thread. While it is true that energy is added to move to a higher orbit, yet 'U', as specified in the problem is negative which implies that the energy added will be -U/4asishkm@gmail.comcfred@mit.eduI don't see the implication.
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8/21/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/Quiz_14/Quiz_14/2Quiz 14, Problem 2 - I am not sure if this statement "You may assume that the friction is not so strong as to force the block off the track after it reaches the top." is suffient to ensure that the block completes one loop. It does ensure that the block completes 3/4 of a loop. Might it be better to add the words "or not reach the bottom of the loop".george@andronov.comcfred@mit.edufixed
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8/21/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/HWK_12/Harmonic_Oscillation_Homework/12Parabolic Potential Well - R >> 1/a should be R << 1/a
george@andronov.comcfred@mit.edufixed
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8/21/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/Quiz_11/Quiz_11/in problem 3, "L" is first used as distance along the rod, then as angular momentum. i would change the first use of "L" to "d". also, units for the answer are not specified.larry.stead@gmail.comcfred@mit.educhanged the angular momentum to have a vector symbol.
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8/22/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/Quiz_11/Quiz_11/Problem statement needs to be reworded. The question asks students to "find the angular momentum of the rod about the axis," but the questions really wants you to find L of the rod and mass system about the axis.gphysics@gmail.comcfred@mit.edufixed
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8/23/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/Unit_13/Mechanical_Energy_of_Orbits/2CheckPoint 1: Energy of Circular Orbits - Part 3 - The correct answer is - U/4 not U/4. To get an answer of U/4 one has to assume that U is the modulus of the potential energy. Given that the potential energy is always negative to get a positive value for the extra energy one must multiply U by minus one.
george@andronov.comzchen22@mit.edufixed
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8/23/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/Unit_13/Mechanical_Energy_of_Orbits/5Illustrative Example: Eccentricity of One-Half./ Apply Energy Conservation at Periapsis - First equation should have a plus sign - Ep = Kp + Up and in the next equation there is a subscript missing. It should be Ep. Also "Thus, the ratio of kinetic energy to potential energy at periapsis is: " to be changed to " . . . the magnitude of potential energy . . . .".george@andronov.comzchen22@mit.educorrected the signs, and changed a sign in the second equation accordingly. Aaa all those negative signs.......
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8/23/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/Unit_14/One_Step_Problems_and_Simultaneous_Models/1The second sentence of the third paragraph should read "For example, in the problem on the next page, the state of the system . . ."mixson1977@gmail.comalwina@mit.edufixed
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8/23/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/Unit_14/One_Step_Problems_and_Simultaneous_Models/2In the "Solution" section, the sentence with the "1. Constant Linear Momentum" label should read "1. Constant Linear Momentum applies to the 2 boxes + spring system:" In the "Solution" section, the sentence with the "2. Constant Mechanical Energy" label should read "2. Constant Mechanical Energy applies to the 2 boxes + spring system:" The fourth to the last sentence in the "Solution" section should read "From (eq. 1) we obtain that the speeds of both boxes are the same."mixson1977@gmail.comalwina@mit.edufixed
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8/23/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/Unit_14/One_Step_Problems_and_Simultaneous_Models/4The first sentence under the section labeled "Condition of minimum speed" should read "To obtain the speed at the bottom we will use the condition about the minimum speed needed at the top in order to make a turn."mixson1977@gmail.comalwina@mit.edufixed
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8/23/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/Unit_14/One_Step_Problems_and_Simultaneous_Models/5In the "Solution:" to "Problem 1:", the first sentence in "Show Algebra:" should read "The trick consists of grouping . . . ."mixson1977@gmail.comalwina@mit.edufixed
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8/24/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/Unit_14/One_Step_Problems_and_Simultaneous_Models/8In the "Solution:" section, under the "Approach:", the statement under the "Final State" diagram should read "t_{f}: Instant right after the ball loses contact with the rod." In the "Solution:" section, under the "Show derivation of (eq. 1):", the equation under the "The final momentum:" should read $\vec{P}^{sys}\left(t_{f}\right)=mv_{f}\hat{i}+m\vec{v}_{rod}=m0.8v_{i}\hat{i}+m\vec{v}_{rod}$. In the "Solution:" section, under "Constant Angular Momentum about point Q:", the final sentence is missing a closing parenthesis: " . . . . does not give any angular momentum about its center of mass, point Q.)" In the section labeled "Show derivation of (eq. 2):", the second to the last sentence has the words "spin component" hyperlinked and when you press the hyperlink, a page comes up that reads "PAGE NOT FOUND." In the "Solution:" section, the first equation under the "Final Mechanical energy:" label should read $E\left(t_{f}\right)=K^{ball}\left(t_{f}\right)+K^{rod}\left(t_{f}\right)$.mixson1977@gmail.comalwina@mit.edufixed
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8/24/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/Unit_14/Multiple_Step_Problems_and_Consecutive_Models/1The third to the last sentence on the page should read "In the illustrative example on the following page, . . . ."mixson1977@gmail.comalwina@mit.edufixed
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8/24/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/Unit_14/Multiple_Step_Problems_and_Consecutive_Models/2In the box labeled "3. Describe the interactions in step 1.", the last sentence under the "2 Boxes + Spring" section should read "We assume a short time collision so the spring remains in equilibrium and it does not exert any force on box 2." In the "2 Boxes" section under "3. Describe the interactions in step 1.", the second to the last sentence should read "The sum of the external forces (gravity and normal) is zero:" In the box labeled "5. Apply the model in step 2:", the second sentence should read "At the instant $t=t_{f}$, the boxes are at rest and the spring is compressed."mixson1977@gmail.comalwina@mit.edufixed
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8/24/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/Unit_14/Multiple_Step_Problems_and_Consecutive_Models/3Under the Solution section, the second box should be labeled "1. Choose the system for each step". In that same section, the categories should be labeled "Steps 1 & 3" and "Step 2". In the section labeled "2. Define the initial and final states of each of the steps", the "Final State of step 2" should read "$t_{2}$: instant right after the ball loses contact with the table". The "Initial State of step 3" should read $t_{2}$: instant right after the ball loses contact with the table". The final sentence should read "The same answer is obtained if the solution to the sub-problems in steps 1 and 3 is obtained using 1-D kinematics models."mixson1977@gmail.comalwina@mit.edufixed
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8/24/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/Unit_14/Multiple_Step_Problems_and_Consecutive_Models/4In the section labeled "How many steps does the problem have?", "Step 2:" should read "The bar falls down rotating about the hinge through an angle of $90^{\circ}$." In the section labeled "2. Define the initial and final states of each of the steps", the label for $t_{1}$ in the diagram should read "Intermediate State". In the section labeled "2. Define the initial and final states of each of the steps", the sentence directly below "Final State of step 1" should read "$t_{1}$: instant right after the collision when the bar loses contact with the ball." In the same section, the sentence directly below "Initial State of step 2" should read "$t_{1}$: instant right after the collision when the bar loses contact with the ball." In the box labeled "Explanation of the zero net external torque:" under the section "3. 4. & 5. Describe the interactions, select and apply the model on each step.", the last sentence should read " . . . ., then its weight and the position vector of the ball measured from the hinge are also along the same line, . . ."mixson1977@gmail.comalwina@mit.edufixed
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8/25/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/Unit_12/Mechanical_Energy_in_SHM/7CheckPoint 3: Energy in SHM - "U stands for potential energy" A student has pointed out that no refernce potential energy has been given. Since the course is trying to dissenimate good practice I suggest "U stands for potential energy which is zero at the equilibrium position."george@andronov.comzchen22@mit.eduActually, I don't think any of the choices depend on the choice of reference point. Adding a specific reference point may mislead students to believe that these results only hold for that choice of reference point. So I would let it stay as it is. Thanks for raising the issue though.
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8/25/2013 https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/HWK_12/Harmonic_Oscillation_Homework/9 https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/HWK_12/Harmonic_Oscillation_Homework/10I know these problems have been checked before but there is something wrong. First it might be the wording.- "The equations below show the positions of two oscillators over time" Should be replaced by "The equations below show the positions of two oscillating particles, A and B, over time". The "Which oscillator" should be replaced by "Which particle". Next for question 10 (Compare Distance from Origin). I am fairly sure the grader is not working correctly.george@andronov.comzchen22@mit.eduIn my opinion, these equations are more generall than "particles". They can describe any oscillating entities such as e-m waves or points on an oscillating beam. So I would leave the wording as it is. As to #10, since it has passed the deadline I cannot test myself if the grader is working or not. However, I don't see anything wrong in the code. But I'll keep an eye for this one next time
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8/26/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/HWK_14/Review_Homework/7The question for the "Projectile Explodes Into Two Fragments Part 2" should read "If the speed of the projectile just before the explosion was $v$, by how much did the kinetic energy of the system increase as the result of the explosion?"mixson1977@gmail.com
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8/29/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/Unit_13/Mechanical_Energy_of_Orbits/6
Keplerian Orbit Model - I can see the picture of the simulation but cannot download the simulation by clicking on the image. The link below the image works.. Reported by a student (and me) when running Firefox.george@andronov.com
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8/29/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/HWK_14/Review_Homework/1Physics Of Unicycling - This is one of a number of items which seem not to work when I use Firefox. There is no image and there are no links shown below where the image would normally be.george@andronov.com
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8/29/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/Unit_12/Pendulums_and_the_Ubiquity_of_SHM/10Pendulum Lab - Here is an exapmle of ano image but the link underneath working when using Firefox on a PC.george@andronov.com
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8/29/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/Unit_13/Mechanical_Energy_of_Orbits/1Mechanical Energy of Orbits - Last paragraph, last sentance "At the periapsis, the potential energy is larger in size than it . . .". Replace size with magnitude - it has confused some students. This is always going to be a problem when the counting is done with negative numbers. On reflection might it be better to write "At the periapsis, the potential energy is smaller than it . . . . ?george@andronov.com
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8/30/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/HWK_13/Orbits_Homework/14Dust Cloud - One of the students has pointed out that in getting to the final answer you are subtracting two large number from one another to get a small number. Because some of the data is only given to 2 significant figures this lead to a large error (300%) in the value of the differnce. I suggest that all the data is given to 5 significant figures. I realise that this error has become much more obvious after the change was made from the data being given as decimals to being in quasi-scientific notation.george@andronov.com
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8/30/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/Unit_14/One_Step_Problems_and_Simultaneous_Models/3Checkpoint 1: Spring and Two Masses - A student has voiced concern about the word of Part 2 - https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/discussion/forum/MReV_Summer2013_BK144/threads/52200ec41e80e9160000000f - I suggest that the question should be changed to something like "What information which is given in the original question will help you find the maximum speed of block m and what further assumptions, if any, will you have to make."george@andronov.com
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9/3/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/HWK_13/Orbits_Homework/3Circular orbits: Forces - student JamieGriffiths claims the grader has incorrectly graded his answer - "My answer which was graded 'incorrect' is the same as the 'show answer' 'correct answer'." - https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/discussion/forum/MReV_Summer2013_circular_force/threads/521e2903703c010a00000002george@andronov.comzchen22@mit.eduNot sure what's caused the problem.
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8/17/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/Unit_11/Applications_of_the_Angular_Momentum_and_External_Torque_Model/Checkpoint 14, Part A: "Center of the midpoint of" could and should be just "midpoint of". CreativeAhaan@gmail.com
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8/22/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/Quiz_11/Quiz_11/Quiz 11, Problem 3: Although the problem says "magnitude" of the angular momentum, it says $\vec{L}$ above the answer box. It should probably say, for very nit-picky reasons, $||\vec{L}||$. CreativeAhaan@gmail.com
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8/22/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/Quiz_11/Quiz_11/Quiz 11, Problem 10: The diagram has "1|" instead of "1".CreativeAhaan@gmail.com
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8/23/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/Unit_12/Kinematics_of_Simple_Harmonic_Motion/Checkpoint 6: Currently marked as Checkpoint 2. Numbering should be fixed. Also, for Part 1 -- maybe speed, not velocity? See my post (Ahaanomegas) for that problem on the discussion boards.CreativeAhaan@gmail.com
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8/23/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/Unit_12/Kinematics_of_Simple_Harmonic_Motion/Checkpoint 7: x_{max} should be LaTeXed.CreativeAhaan@gmail.com
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8/24/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/Unit_12/Pendulums_and_the_Ubiquity_of_SHM/Checkpoint 6: Two pendula -- random "x"s in diagram. CreativeAhaan@gmail.com
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8/24/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/HWK_12/Harmonic_Oscillation_Homework/Parabolic Potential Well -- I'd like it LaTeXed: $y=ax^2$. Also, the diagram and extra parentheses make it seem like v = a^2, where a is a function of x: a(x). It should probably just be $ y = ax^2 $ or $ y = a \cdot x^2 $. CreativeAhaan@gmail.com
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8/25/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/Unit_13/Mechanical_Energy_of_Orbits/Keplerian Orbit Model: The image link does not exist. The comPADRE link is fine.CreativeAhaan@gmail.com
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8/25/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/discussion/forum/MReV_Summer2013_Damped_and_Driven_Ha/threads/521a2cb965fb890e0000000dDamped and Driven Harmonic Oscillations: There is an "x" missing in the second derivative with respect to time in this chapter:

$ m \cdot \dfrac {d^2}{dt^2} = -kx + F_0 \cos (\omega \, \mathrm{d}t) $ and, later, $ m \cdot \dfrac {d^2}{dt^2} +kx=F_0 \cos(\omega \, \mathrm{d}t) $. 		CreativeAhaan@gmail.com
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8/25/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/HWK_13/Orbits_Homework/Problem 14: Dust Cloud. For each x in the scientific notation, it should have either $\cdot$ or $\times$. CreativeAhaan@gmail.com
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8/25/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/HWK_13/Orbits_Homework/Problem 5, Orbital Transfer: Satellite is misspelled in the second paragraph. CreativeAhaan@gmail.com
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8/28/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/Unit_13/Keplerian_Orbit_Model/21Checkpoint numbers messed up. There is a Checkpoint 12 and a Checkpoint 14, but no Checkpoint 13.CreativeAhaan@gmail.com
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8/29/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/HWK_14/Review_Homework/17Problem 17: "As an engineer for amusement park" should be "As an engineer for an amusement park". CreativeAhaan@gmail.com
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8/30/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/Unit_13/To_the_Moon/1Under 'Interactions' it should be the mass of the moon, not earth. CreativeAhaan@gmail.com
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9/1/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/Quiz_13/Quiz_13/3The angle in the diagram is marked as $\alpha$, but the same angle is referred to as $\theta$ in the question. They need to have the same name. CreativeAhaan@gmail.com
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9/1/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/Unit_14/One_Step_Problems_and_Simultaneous_Models/Checkpoint 3 (Pendulum): Part 2 -- "At the instant ball passes its lowest position" should be "At the instant that the ball ..."CreativeAhaan@gmail.com
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9/3/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/HWK_13/Orbits_Homework/15Homework 13, Last Problem: Show Answer(s) button doesn't show answer.CreativeAhaan@gmail.comzchen22@mit.eduUnfortunately the "show answer" button doesn't work for the drag and drop problems.
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9/4/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/Unit_14/Multiple_Step_Problems_and_Consecutive_Models/4Should say State not Sate.CreativeAhaan@gmail.comzchen22@mit.eduUmmm....can't find the type, Can you be more specific?
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9/6/2013https://courses.edx.org/courses/MITx/8.MReV/2013_Summer/courseware/Unit_14/One_Step_Problems_and_Simultaneous_Models/7A meteor approaching a planet - Under Solution -> Approach -> Show derivation of eq. 1 there are links "spin component" and "orbital component" which do not open.george@andronov.comzchen22@mit.edu"Module3" in folder Unit14 missing completely.
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