Question

Calculate the work done by the brakes of a car of mass 1000kg when its speed is reduced from 20m/s to 10m/s

Answer 1

Given:
u = 20 m/s
v = 10 m/s
m = 1000kg
Work done = 1/2*m*(v²-u²)
                  = 1/2 * 1000*(10²-20²)
                  = 500 * (100-200)
                  = 500 * (-100)
                  = -50000 J