Question

A car of mass 900 kg is traveling at 20 m/s when the brakes are applied. The car then comes to a complete stop in 5 s. What is the average power that the brakes produce in stopping the car?

A. 36,000 W
B. 7200 W
C. 3600 W
D. 1800 W

Answer 1

A. 36,000 W

Step-by-step explanation:

`m` = mass of the car = 900 kg

`v_(o)` = Initial speed of the car = 20 m/s

`v_(f)` = Final speed of the car = 0 m/s

`W` = Work done by the brakes on the car

Magnitude of work done on the car by the brakes is same as the change in kinetic energy of the car.hence

`W = (0.5) m (v_(o)^(2) - v_(f)^(2))\\W = (0.5) (900) ((20)^(2) - (0)^(2))\\W = 180000 J`

`t` = time taken by the car to come to stop = 5 s

`P` = Average power produced by the car

Average power produced by the car is given as

`P = (W)/(t) =(180000)/(5) \\P = 36000 W`