Question

A motorist travelled at 90km/hour applied it's brake came to rest with uniform retardation in 20seconds, calculate the retardation in meter per seconds square

Answer 1

Given:

$v_i=90\:\rm km/h=25\: m/s$

$v_f=0\:\rm km/h=0\: m/s$

$\Delta t=20\:\rm s$

The retardation

$$a=\frac{\Delta v}{\Delta t}=\frac{0-25}{20}=-1.25\:\rm m/s^2$$