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 ($g=10m{s}^{-2}$).The coefficient friction between the road and the tyres is:

• A. $0.33$
• B. $4.5$
• C. $0.67$
• D. $0.8$

Answer 1

Answer: (C)

$0.67$

Velocity of the car = $72kmph=20m/s$
Also,
$v^2-u^2=2\mu gs$
$\therefore \mu =\frac{-u^2}{2gs}$
$=\frac{{20}^2}{2\times 10\times 30}$
$=0.67$