What is kinetic energy and how do we calculate it?

Retrieval practice:

• What is the equation for work done?
• Calculate the work done by a person lifting a weight of 420N to a height of 1.8m.
• What is gravitational potential energy?
• How is gravitational potential energy (E_p) calculated?
• Calculate the E_p when a ball with mass 0.4kg is kicked 20m in the air assuming gravity is 10N/kg
• What is kinetic energy?

Challenge:

Suggest what factors determine the size of an object’s kinetic energy.

Quiet time task one:

• Please complete the key question calculations on page 9-11
• Complete the practice problem questions on pages 13 to 18

Challenge:

Calculate the gravity on a planet, if an object with a mass of 125kg has 17.5KJ of potential energy when it is at a height of 75m.

Challenge:

Suggest what factors determine the size of an object’s kinetic energy.

What is kinetic energy and how do we calculate it?

Retrieval practice:

• Calculate the E_p when a ball with mass 0.8kg is kicked 60m in the air assuming gravity is 9.8N/kg
• What is kinetic energy?
• Suggest two factors that will impact the amount of kinetic energy an object has.
• A force is applied to a ball with a mass of 1.5kg that causes the ball to accelerate at 1.7m/s², the force is applied over a distance of 1.8m, calculate the work done by the person applying the force.

Challenge:

An object with mass 2500kg reaches a terminal velocity of 24m/s, when a force of 3kN is applied, the acceleration occurs over 40m, calculate the initial velocity.

What is kinetic energy and how do we calculate it?

Retrieval practice: (On MWBs)

• What is gravitational potential energy?
• Use the equation: Ep= m x g x h Calculate the E_p when a ball with mass 0.4kg is kicked 20m in the air assuming gravity is 10N/kg
• What is kinetic energy?
• Which do you think has more kinetic energy: A elephant running or a bullet fired out of a gun?

Challenge:

Suggest what factors determine the size of an object’s kinetic energy.

Kinetic Energy (E_k):

• Kinetic energy is the energy of movement, it is determined by two factors:
• The object’s mass
• The object’s velocity

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• For example:
• Two objects with identical masses, travelling at identical velocities will have exactly the same kinetic energy.

Kinetic Energy (E_k):

• Kinetic energy is the energy of movement, it is calculated using the mass and velocity of an object.

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• The equation for kinetic energy is:
• E_K = ½ m x v²

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• Kinetic energy = ½ x mass x velocity²
• Joules Kg m/s

A worked example

A Giraffe has a mass of 800 kg and is running at a velocity of 20 m/s. What is it’s KE?

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• E_K = ½ mass x velocity²

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• E_K = 0.5 x 800kg x 20² m/s

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• E_K = 0.5 x 800 x 400

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• E_K = 160,000J

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Rearranging the equation:

An Eagle had the 405J of KE, when it was flying at 18m/s, calculate the mass of this Eagle.

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• E_K = ½ mass x velocity²
• 405 = 0.5 x m x 18² m/s (therefore)
• 405 ➗ (0.5 x 18²) = m or 405 ➗ (0.5 x324)
• m = 2.5kg

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Quiet time task one:

• Complete the questions on kinetic energy from pages 17-20

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Challenge:

Use both E_p and E_k equations to calculate the maximum velocity a ball with a mass of 1.5kg could reach if dropped from a height of 12m (assume gravity = 10N/kg)

What is kinetic energy and how do we calculate it?

Retrieval practice:

• Calculate the work done by a person lifting a weight of 260N to a height of 2.7m.
• Calculate the E_p when a ball with mass 0.35 kg is kicked 45m in the air assuming gravity is 10N/kg
• What is kinetic energy?
• What is the equation for calculating kinetic energy?
• Calculate the kinetic energy of a human with mass 100kg, walking at 2m/s/

Calculate the gravity on a planet, if an object with a mass of 125kg has 17.5KJ of potential energy when it is at a height of 75m.

Was is gravitational potential energy?

Gravitational potential energy Store is the amount of energy an object has because of its position above the ground, when placed in a gravitational field i.e. its height.

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The equation for gravitational potential energy is:

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E_P= m x g x h

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Was is gravitational potential energy? Recap

• Mass is measured in kilograms (kg).
• Gravitational field strength is measured in newtons per kilogram (N/kg), usually taken as 10 N/kg on Earth.
• Height is measured in metres (m).
• E_p (GPE) is measured in joules (J).
• Don’t forget! You should convert units (e.g. km to m) to make sure you have the right units for the equation.

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A worked example

As osprey has a mass of 2kg and is flying at a height of 200m. What is it’s E_P ?

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• E_P = m x g x h (always write the equation out first)

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• E_P = 2kg x 10N/kg x 200m

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• =4,000J of E_P (show units!!)

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What is kinetic energy and how do we calculate it?

Retrieval practice:

• What is the golden rule for the conservation of energy.
• What is kinetic energy?
• What two factor determine an object’s kinetic energy?
• What is the equation for calculating kinetic energy?
• Calculate the kinetic energy of a human with mass 100 kg, walking at 2m/s/

Calculate the gravity on a planet, if an object with a mass of 125kg has 17.5KJ of potential energy when it is at a height of 75m.

Quiet time task:

Complete sample questions on pages 19-22 of the booklet.

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Challenge:

Calculate the velocity of a car that has a kinetic energy of 157,500 J when it has a mass of 1400 kg

Retrieval practise:

• What is the equation used to calculate gravitational potential energy?
• What is the equation used to calculate kinetic energy?
• If Maria lifts a mass of 10 kg onto a table 1.25 m high. How much G.P.E. has the mass gained? (assuming g= 9.8N/kg)
• Calculate the kinetic energy in a car with a mass 1200 kg, when it is travelling at 12m/s.
• Calculate the mass of a car that has an E_k of 70,000J when it is travelling at 10 m/s,

Challenge: Explain why the tallest point on a rollercoaster is always at the start.

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Challenge:

An object with mass 1800kg reaches a terminal velocity of 17m/s, when a force of 2.4kN is applied, the acceleration occurs over 80m, calculate the initial velocity.

What is kinetic energy and how do we calculate it?

Retrieval practice: On MWBs

• What is the golden rule for the conservation of energy.
• Name three ways energy can be transferred from one place or store to another.
• Complete the following sentences:
• ______________ energy is the energy stored in a moving object. It is determined by the mass and the __________ that the object is moving.
• Gravitational ____________ energy, is the energy in objects that are high up, these objects have the potential to ____________.

Going off booklet

• Today we are going to compare your personal power output during two different exercises.
• Exercise one: Step up (endurance 1 minute)
• Exercise two: Stair sprint (as fast as you can)
• For this we need to know the work done and the time taken
• To calculate these we need to know the force in Newtons (you can either find this accurately or use 600N)
• We will need to measure the distance.
• We will need to record the time.

Step up power calculation

• Need to Measure the height of the step used.
• Count the number of steps in one minute
• Need to know the force (weight) of the participant

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Calculation of work done = Force x distance

Therefore:

Work = (Force x number of steps x height of step)

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Power = Work done / time (60s)

Step up power calculation

• Need to Measure the height of the staircase
• Time how long it takes to get to the top.
• Need to know the force (weight) of the participant

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Calculation of work done = Force x distance

Therefore:

Work = (Force x number of steps x height of step)

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Power = Work done / time

Using the two equations together….

“Calculate the final velocity of an object that has a mass of 20kg, and falls from a height of 5m”

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• Step one calculate the change in GPE GPE= m x g x h
• GPE= 20 x 10 x 5
• GPE = 1000J
• Step two convert that into KE (assume none is wasted)
• 1000J of GPE = 1000J of KE
• Step three Calculate velocity
• KE= ½ x m x v² 1000= ½ x 20 x v²
• v²= KE ÷ ½ x m 1000 ÷ 10 = v²
• √v² = v √ 100 = v v= 10

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11:00 AM

What is kinetic energy and how do we calculate it?

Retrieval practice:

• Calculate the gravitational potential energy of an object that is 6.5m above the ground, if it has a mass of 30kg.
• For the same object as question 1 calculate how high it would need to be to have a gravitational potential energy of 6000J?
• Calculate the kinetic energy of a motorbike that has a mass of 250 kg if it is travelling at 25m/s.
• Calculate the new velocity of the motorbike, if it now has 12500 J of kinetic energy.

Challenge:

Explain the pattern of reactivity down group one.

Describe what happens in a displacement reaction.

Quiet time task:

Exam Practise Questions:

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Please attempt the exam style questions pages 24- 32

Have a go at these questions in your book:

• If Maria lifts a mass of 10 kg onto a table 1.25 m high. How much G.P.E. has the mass gained?

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• If Sophie climbs a ladder 3.4 m tall, and Sophie has a mass of 48 kg, how much G.P.E. has she gained?

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• A man of mass 80 kg standing at the top of a tall building has 96000 J of G.P.E. How tall is the building?

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• How much G.P.E. would the man in question 3 have if the same building were on the moon? (g = 1.6 N/kg on the moon)

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11:00 AM

Calculating KE:

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• A year 11 pupil with a mass of 55kg swinging back on their chair and falling off it at a speed of 0.6m/s.
• A runner with a mass of 62kg running at a speed of 0.8m/s.
• A tennis ball travelling at a speed of 46m/s with a mass of 58kg.
• A dog running across a field at a speed of 1.2m/s with a mass of 3.2kg.

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Calculating velocity:

• Bus travelling through town, with a mass of 5040kg and kinetic energy of 493900J.
• A lift travelling up to the top floor of the Empire State building with a mass of 4200kg and a kinetic energy of 4116J.
• Bird flying towards its nest with a mass of 0.25kg and a kinetic energy of 40.5J.

Calculating mass

• Automatic door closing 0.2m/s, with a kinetic energy of 1.6J.
• Wind turbine blade with a kinetic energy of 104040J, turning at 6m/s.
• Canoe moving down the river with a kinetic energy of 5J and a speed of 0.5m/s.

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Monday, 05 December 2016�Kinetic energy and GPE summary

11:00 AM

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• What is the equation for calculating kinetic energy?

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• Copy the diagram into your book, using a letter X mark where you think the cart has the most GPE, use a Y to show where you think it has the most KE

Monday, 05 December 2016�Kinetic energy and GPE summary

11:00 AM

Starter:

• What is the equation for calculating kinetic energy?

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• Copy the diagram into your book, using a letter X mark where you think the cart has the most GPE, use a Y to show where you think it has the most KE

X

Y

Monday, 05 December 2016�Kinetic energy and GPE

LO: To be able to describe the relationship between KE and GPE in different scenarios

11:00 AM

Starter:

• At position A the Car has lots of gravitational potential energy, why?

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• Describe the energy transfer that has happened between points A and B.

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• Why can the second hill not be as big as the first hill on the rollercoaster?

Using the two equations

GPE: (GPE = m x g x h)

• A woman standing on a bridge 25m tall has a mass of 55kg. Calculate her GPE

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• Calculate how high the bridge would have to be on the moon (g= 1.6N/kg) for her to have the same amount of GPE.

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• Calculate the mass of an object that has 3000J of GPE when at a height of 15m.

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11:11 AM

KE: (KE= ½ x m x V²)

• A year 11 pupil with a mass of 55kg swinging back on their chair and falling off it at a speed of 0.6m/s.

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• A dog running across a field at a speed of 1.2m/s with a mass of 3.2kg.

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• Wind turbine blade with a kinetic energy of 104040J, turning at 6m/s

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• Bus travelling through town, with a mass of 5040kg and kinetic energy of 493900J.

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Using the two equations together….

“Calculate the final velocity of an object that has a mass of 36kg, and falls from a height of 10m”

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• Step one calculate the change in GPE GPE= m x g x h
• Step two convert that into KE (assume none is wasted)
• Step three Calculate velocity

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2:14 PM

Questions:

Calculating KE:

• A car that travels at a speed of 20m/s and has a mass of 1200 kg.
• A year 11 pupil with a mass of 55kg swinging back on their chair and falling off it at a speed of 0.6m/s.
• A runner with a mass of 62kg running at a speed of 0.8m/s.
• A tennis ball travelling at a speed of 46m/s with a mass of 58kg.
• A dog running across a field at a speed of 1.2m/s with a mass of 3.2kg.

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Calculating velocity:

• Bus travelling through town, with a mass of 5040kg and kinetic energy of 493900J.
• A lift travelling up to the top floor of the Empire State building with a mass of 4200kg and a kinetic energy of 4116J.
• Bird flying towards its nest with a mass of 0.25kg and a kinetic energy of 40.5J.

Calculating mass

• Automatic door closing 0.2m/s, with a kinetic energy of 1.6J.
• Wind turbine blade with a kinetic energy of 104040J, turning at 6m/s.
• Canoe moving down the river with a kinetic energy of 5J and a speed of 0.5m/s.

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Using the equations…

Write down the equations for each of the following:

• Calculating work done
• Calculating GPE
• Calculating KE
• Calculating energy efficiency

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11:00 AM

• Calculate the work done by an electric crane that lifts a container that weighs 25000N, 15m into the air.

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• The crane used 500,000J of electrical energy to lift the container, calculate the efficiency of this transfer.

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• Calculate the GPE of the container once it has been lifted.

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• If the container was dropped what would be the final velocity of the container?

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Energy: Skills recap lesson

• State the equations used to calculate each of the following, gravitational potential energy, kinetic energy.
• Calculate the gravitational potential energy of an object that is 6.5m above the ground, if it has a mass of 30kg.
• For the same object as question 2 calculate how high it would need to be to have a gravitational potential energy of 6000J?
• Calculate the kinetic energy of a motorbike that has a mass of 250kg if it is travelling at 25m/s.
• Calculate the new velocity of the motorbike, if it now has 12500 J of kinetic energy.

Challenge:

If an object with a mass of 25kg is dropped from a height of 20m calculate the maximum velocity it will achieve, assuming the energy transferred 100% efficiently.

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AO2 and AO3 style questions:

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Please complete the exam style questions from page 17-21

Challenge:

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If an object with a mass of 2.5g is dropped from a height of 21m calculate the maximum velocity it will achieve, assuming the energy transferred 100% efficiently.

Starter:

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Please complete the AO2 and AO3 style questions from page 17-21

Challenge:

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If an object with a mass of 2.5g is dropped from a height of 21m calculate the maximum velocity it will achieve, assuming the energy transferred 100% efficiently.

Specific heat capacity

• State the equation that uses the specific heat capacity of a material to calculate energy transferred.
• Calculate the energy transferred by a heater, if the heater raises the temperature of 2kg of water by 12℃, (SHC of Water = 4200J/kg℃).
• Calculate the energy transferred by a heater, if the heater raises the temperature of 250g of water by 50℃, (SHC of Water = 4200J/kg℃).
• Calculate the specific heat capacity of a material when 2kg of the material are heated by 14℃ when 650J are transferred to it.
• Calculate the specific heat capacity of a material when 1.5kg of the material are heated by 17℃ when 2800J are transferred to it.
• Calculate the temperature change that will occur when 2500J are transferred to 1kg of a material with a specific heat capacity of 240J/kg℃

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For challenge see the whiteboard at the back.

Ensure the all key questions are complete first.

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AO2 and AO3 style questions:

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Please complete the exam style questions from page 25 onwards.

Challenge:

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Calculate the final temperature if 8000J are transferred to a bowl of ice water. The mass of the ice water is 450g.