Question

A scooterist moving with a speed of 36km/h sees a child standing in the middle of the road. He applies the brakes and brings the scooter to rest in 5s just in time to save the child. Calculate the average retarding force on the vehicle, if mass of the vehicle and the driver is 300kg.

(a) 270N

(b) 600N

(c) 150N

(d) 125N

The question was asked during an interview for a job.

This is a very interesting question from Gravity in portion Laws of Motion of Engineering Physics I

Answer 1

Right answer is (b) 600N

The best explanation: u = 36km/h = 10m/s, v = 0, t = 5s

a = (v-u)/t = (0-10)/5 = -2m/s^2

Retardation = 2m/s^2

Average retarding force = 300×2 = 600N.