Conservation of Energy (Edexcel GCSE Physics)

Which of these is a non-renewable source of energy?

Explain why renewable sources provide an increasing fraction of the electricity supply for many countries.

Electricity can be generated using a water turbine.

i) Water gains kinetic energy by falling from the top of a dam.

Calculate the minimum height that 7.0 kg of water must fall to gain 1300 J of kinetic energy.

minimum height = ........................................................... m[3]

ii) As water enters the turbine at the bottom of the dam, the kinetic energy of 8.0 kg of moving water is 1100 J.

Calculate the speed of the moving water as it enters the turbine.

speed = .......................................................... m/s[3]

Moving air can be used to generate electricity using a wind turbine.

Figure 8 is a graph of kinetic energy against wind speed for a mass of moving air.

Figure 8

Just before the air reaches a wind turbine it has a wind speed of 15 m/s.

When the air has gone through the turbine it has a wind speed of 13 m/s.

As the air moves through the turbine some of the energy in its kinetic store is transferred to the turbine's kinetic store.

Use the graph to determine the percentage of the energy in the wind's kinetic store transferred to the turbine from the air.

percentage of energy transferred from the air's kinetic store = ................. %

Figure 5 shows a way of projecting a small trolley up a sloping track.

Figure 5

When the button is pressed, a spring is released in P that projects the trolley up the track.

The trolley travels up the track, stops and then rolls back down.

The spring in P always exerts the same force when projecting the trolley.

A student investigates how the mass of the trolley affects the maximum vertical height, h, reached by the trolley.

State the measurements the student should make to complete the investigation.

You should make use of the equipment shown in Figure 5 and any other equipment that is needed.

Figure 6 is a graph of the student’s results.

Figure 6

The student states that the energy transferred by the spring is the same each time it is used.

Use data from any two points on the graph in Figure 6 to support this statement.

Describe how the student could extend the investigation to determine the average speed of the trolley as it rolls back down the track.

Figure 1 shows a person on a zip wire. The person's weight is 650 N.

Figure 1

The person has 15 000 J in their gravitational potential store at the top of the tower.

Determine the vertical height of the tower.

 height = ................................... m

The height of the zip rope at the end of the ride is 2.5 m above ground.

Determine the change in gravitational potential energy over the course of the zip rope ride.

 change in gravitational potential energy ..................... J

Determine the mass of the rider.

Give your answer to the nearest kg.

 mass =  .................................... kg

Determine the speed of the rider just before they reach the end of the zip rope.

Ignore any frictional forces.

Figure 1 shows a cyclist riding down an incline.

Figure 1

Use words from the box to complete the following sentences.  

As the cyclist rides down the hill, the amount of energy in his .............................. store decreases.

As the cyclist accelerates, energy in his .............................. store increases.

When the cyclist uses his breaks to stop, energy is transferred to the .............................. store of the brake pads.

The cyclist descends the hill without braking.

The hill the cyclist rode down has a vertical height of 23.5 m.

20 kJ of energy was transferred from the cyclist's gravitational potential energy store as he rode from the top of the hill to the bottom.

Determine the mass of the cyclist.

Give your answer to 3 significant figures.

   mass of cyclist  = .................................... kg

Calculate the maximum speed of the cyclist during his descent.

Ignore any energy losses.

Give your answer to 1 significant figure.

  maximum speed = .................................... m/s

In reality, the cyclist only achieved a maximum speed of 12 m/s.

Calculate the percentage efficiency of the cyclist. 

 efficiency =  .................................... %

A small plastic ball is held at a height, , above the ground.

The ball is released and takes 2.34 s to fall to the ground.

Calculate the distance the ball travelled during its fall. Ignore any energy losses.

Use the equation

 distance =  .................................... m

Describe the energy transfer taking place as the ball is released and falls.

The ball was dropped repeatedly from the same height, but the measured time taken was different for each repeat. 

(i) Suggest why the time measured was different for each repeat.

[1]  

(ii) Suggest how to improve the accuracy of the measurement.

[1]

A different ball of mass 23 g is dropped from the same height.

(i) Calculate the change in gravitational potential energy as the ball falls.

change in gravitational potential energy = ............................ J [3]

(ii) State the energy transfer that occurs at the moment the ball hits the ground.

[2]

A student lifts a toy car from a bench and places the toy car at the top of a slope as shown in Figure 2.

Figure 2

Describe an energy transfer that occurs when the student lifts the toy car from the bench and places the toy car at the top of the slope.

The student lets the toy car roll down the slope.

Describe how the student could find, by experiment, the speed of the toy car at the bottom of the slope.

The student needs to develop the experiment to determine the loss in potential energy and the gain in kinetic energy as the toy car is rolling down the slope.

State the other measurements the student must make.

When the toy car rolls down the slope, some energy is transferred to the surroundings as thermal energy.

State how the student could calculate the amount of energy transferred to the surroundings.