 GCSE Questions: Forces Q5. A child drops a ball. The ball hits the ground and bounces.

The graph is a velocity-time graph for the ball from t = 0.0s, when the ball was dropped, until t = 1.2s, when the ball reaches the top of its first bounce. Air resistance has been ignored. (a) Describe the motion of the ball between points A and B on the graph.

The ball moves downwards at a uniform acceleration.  The word 'describe' means you are not expected to do calculations.

[3 marks]

(b) In what direction is the ball moving between points C and D on the graph?

Upwards [1 mark]

(c) The ball and the Earth form a system.

What is meant by 'a system'?

Tick one box in the table below to answer.

 Statement Tick here A group of objects that interact. Objects with big differences in mass. Objects with gravitational potential energy.

[1 mark]

(d) When the ball hits the ground, energy is transferred from the ball to the Earth.

Explain how the data in the graph shows this energy transfer.

The ball hits the ground at point B.

Its kinetic energy is changed into elastic energy within the ball which then is transferred to kinetic energy in the ball at point C - making it change direction on impact and accelerate upwards.

However, the initial velocity of the ball after impact is -5 m/s not -7 m/s, so its kinetic energy after the bounce is less than it was just before. Some of the energy was therefore not transferred back to the ball but went into the Earth. This would probably have been transferred to heat and sound (vibrational) energy. The total energy of the system would be conserved but the bounce allowed some of the energy to be transferred from the ball to the Earth.

[4 marks]

[9 Marks TOTAL]