• Jason is doing a bench press, and he slowly pushes the bar up a distance of 0.30 m while pushing upwards on the bar with a force of 200 N. The bar moves with a constant velocity during this time.
• During the upward push, how much work does Jason do on the bar?

1. 60 J
2. 120 J
3. 0 J
4. -60 J
5. -120 J

Question 7.1

Initial:

Final:

• Jason is doing a bench press, and he slowly lowers the bar down a distance of 0.30 m while pushing upwards on the bar with a force of 200 N. The bar moves with a constant velocity during this time.
• During the downward lowering, how much work does Jason do on the bar?

1. 60 J
2. 120 J
3. 0 J
4. -60 J
5. -120 J

Question 7.2

Initial:

Final:

• Jason is doing a bench press, and he slowly lowers the bar down a distance of 0.30 m while pushing upwards on the bar with a force of 200 N. He then pushes it up slowly the same distance of 0.30 m back to its starting position, also pushing upwards on the bar with a force of 200 N.
• During the complete downward and upward motion, how much total work does Jason do on the bar?

1. 60 J
2. 120 J
3. 0 J
4. -60 J
5. -120 J

Question 7.3

Initial:

Final:

Three balls are thrown from a cliff with the same speed but at different angles. Which ball has the greatest speed just before it hits the ground?

1. Ball A.
2. Ball B.
3. Ball C.
4. All balls have the same speed.

Question 7.4

A hockey puck sliding on smooth ice at 4 m/s comes to a 1-m-high hill. Will it make it to the top of the hill?

QuickCheck 10.9

1. Yes.
2. No.
3. Can’t answer without knowing the mass of the puck.
4. Can’t say without knowing the angle of the hill.

Question 7.5

A car starts with speed v_i, but the driver puts on the brakes and the car slows to a stop. As the car is slowing down, its kinetic energy is transformed to

1. gravitational potential energy.
2. elastic potential energy.
3. internal thermal energy.
4. rest energy.

Question 7.6

Question 7.7: Multiple Answers!

• Yesterday in my office I pushed a box, initially at rest, across the carpet to the other side of my office, where it now rests.
• Define the system to be the box and the carpet. Define the box to have zero height when it is on the floor.
• The initial situation is just before I pushed the box, and the final situation is just after I stopped pushing the box.
• Of all the following quantities, which are not zero? [Choose all that apply]

A ball is thrown directly upward.

At time t₁ it passes a specific height y₁ on the way upward.

At time t₂ it passes the same height y₁ on the way downward.

How does the kinetic energy of the ball at time t₁ compare to t₂?

​[Neglect air resistance in this question.]

• Question 7.8

1. The kinetic energy is the same.
2. The kinetic energy is the different.

Rita raises a 10 kg package at constant speed to a height of 2.5 m in 2.0 s.

​

If she were to raise the same package to the same height in 1.0 s rather than 2.0 s, how would the work and power change?

• Question 7.9

1. the work and power would both stay the same
2. the work would stay the same, but the power would double
3. the work would stay the same, but the power would be half
4. the work would double, but the power would stay the same
5. the work and power would both double

A sports car accelerates from zero to 30 mph in 1.5 s.

How long does it take for it to accelerate from zero to 60 mph, assuming the power of the engine to be independent of velocity and neglecting air resistance?

1. 2 s
2. 3 s
3. 4.5 s
4. 6 s
5. 9 s
6. 12 s

• Question 7.10

Which gas listed below contributes the most to the greenhouse effect that sets the temperature of the Earth?

• Question 7.11

1. Carbon Dioxide
2. CFCs
3. Methane
4. Nitrous Oxide
5. Water Vapor