Question

A car having a mass of $1000\text{kg}$ is moving at a speed of $30\text{m/s}$ . Brakes are applied to bring the car to rest. If the frictional force between the tyres and the road surface is $5000\text{N}$ , the car will come to rest in

• A. $5\text{s}$
• B. $10\text{s}$
• C. $12\text{s}$
• D. $6\text{s}$

Answer 1

The correct option is D $6\text{s}$

Given final velocity $v=0$, initial velocity $u=30\text{m/s}$
By Newtons equation $F_{friction}=ma,a=-\frac{5000}{1000}=-5{\text{m/s}}^2$

From the first equation of motion

$v=u+at\Rightarrow 0=30+(-5)t$ $t=6\text{s}$