Question

Consider a car moving on a straight road with a speed of $100m/s$. The distance at which car can be stopped (${\mu }_k=0.5$)

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

Answer 1

The correct option is D $1000m$

$\begin{array}{c}\mu =100m/s\\ \mu =0.5\\ g=10/s^2\end{array}$

when car is stopped by friction retarding force is

$\begin{array}{c}ma=\mu R\\ ma=\mu mg\\ a=\mu g\end{array}$

Let car covers '5' distance with velocity $\mu$ and stop

$\begin{array}{c}{V}^2-4^2=2aS\\ 4^2=2aS\left(V=0\right)\\ S=\frac{4^2}{2a}=\frac{{100}^2}{2\times \mu g}=\frac{{100}^2}{2\times 0.5\times 10}\\ \Rightarrow S=1000m\end{array}$