Question

A car running with a velocity $72$ $kmph$ on a level road, is stopped after travelling a distance of $30$ $m$ after disengaging it's engine. If the car has a stopping distance of $80$ $m$ on cement road then ${\mu }_k$ is ($g=10m/s^2$):

• A. $0.2$
• B. $0.25$
• C. $0.3$
• D. $0.35$

Answer 1

The correct option is B $0.25$

We have,
$u=72kmph=20m/s$
$v^2-u^2=2{\mu }_{k}gs$
$\therefore {\mu }_k=\frac{u^2}{2gs}$
$\therefore {\mu }_k=\frac{{20}^2}{2\times 10\times 80}$

$=0.25$