PHYSICS · Multi-part · A Level · Physics · Mechanics and materials · Mechanics and materials
Problem
Two cars are moving along the same straight road.
Car A: mass 1000kg, speed 20m/s
Car B: mass 1500kg, speed 15m/s
Answer the following questions:
(a) Calculate the kinetic energy of each car and state which car has the greater value. By how much does it exceed the other?
(b) Both cars apply their brakes and come to rest. Calculate the magnitude of the work done by the brakes on each car.
(c) Suppose that instead of stopping completely, Car A reduces its speed from 20m/s to 10m/s. Find the percentage decrease in its kinetic energy.
(d) Using your result from part (c), comment on how the kinetic energy of a body changes when its speed is reduced to half of the original value.