3.1 Conservation of Energy

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.

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.

Determine the mass of the rider.

Give your answer to the nearest 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

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.

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.

Ignore any energy losses.

Give your answer to 1 significant figure.

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

Calculate the percentage efficiency of the cyclist. 

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

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

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

[2]

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.

[4]

(2)

(1)