Practise calculating momentum change in rebounds, finding collision force from contact time, and explaining how longer stopping time reduces impact force.
A toy rocket is made from a plastic bottle that contains some water.
Air is pumped into the vertical bottle until the pressure inside forces water and air out of the bottle. The bottle then travels vertically upwards.
The air-water mixture is called the propellant.
The variation with time of the vertical velocity of the bottle is shown.
The bottle reaches its highest point at time on the graph and returns to the ground at time . The bottle then bounces. The motion of the bottle after the bounce is shown as a dashed line.
The bottle bounces when it returns to the ground.
The mass of the bottle is 27 g and it is in contact with the ground for 85 ms .
Determine the average force exerted by the ground on the bottle. Give your answer to an appropriate number of significant figures.
The maximum height reached by the bottle is greater with an air-water mixture than with only high-pressure air in the bottle.
Assume that the speed at which the propellant leaves the bottle is the same in both cases.
Explain why the bottle reaches a greater maximum height with an air-water mixture.