Question

A car of mass 200 kg is moving with a velocity of 25 m/s. Brakes are applied and the car comes to rest in 5 s. Find (i) the retardation (ii) the magnitude of force used to stop the car.

Answer 1

Given:-

→Mass of the car=200kg

→Initial velocity of the car=25m/s

→Time taken to come to rest=5s

To find:-

→The retardation

→Magnitude of force used to stop the car

Solution:-

The final velocity of the car will be zero as it finally comes to rest after application of brakes.

By using the 1st equation of motion,we get:-

=>v=u+at

=>a=v-u/t

=>a=0-25/5

=>a= -5m/s²

Since acceleration of the car is -5m/s²,thus the retardation of the car is 5m/s².

Now,by using Newton's 2nd law of motion,we get:-

=>F=ma

=>F=200(-5)

=>F= -1000N

Thus:-

→Retardation of the car is 5m/s².

→Magnitude of force is -1000N,or a

retarding force of 1000N