Question number . 1?

Question

a truck running at 90km/h,slows down to 54km/h over distance of 20m.calculate retardation produce by its brake and time for which the brakes are applied

Answer 1

kinematics says: v^2-u^2=2as

where

v= final velocity = 54kmph 15m/sec

u=initial velocity = 90 kmph = 25 m/sec

s=20m

therefore

225-625= 40a

a= -10m/sec^2