Question

A car is moving on a straight road with a speed 100 ms${}^{-1}$. The distance at which car can be stopped is $[$Take ${\mu }_k=0.5$, $g=10m{s}^{-2}]$

• A. 800 m
• B. 1000 m
• C. 100 m
• D. 400 m

Answer 1

The correct option is B 1000 m

For the car to be stopped by friction, work done against frictional force is equal to change in kinetic energy.

$W_f=K_2-K_1$

$W_f=K_1=0.5m{v}^2$

$\mu mg\left(s\right)=0.5m{v}^2$

$s=\frac{0.5v^2}{\mu g}=\frac{0.5\left({100}^2\right)}{0.5\left(10\right)}=1000m$

Option B.