Question

What is the shortest distance in which an automobile travelling on a 100km/hr can be stopped. (a) when the friction between the tyre and the road is 0.5 (b) on a wet day when the coefficient of friction is only 0.3

Answer 1

$s=\frac{v^2}{2a}$

$F=ma\to a=F/m=\mu mg/m=\mu g$

$100\ km/hr=27.8\ m/s$

(a) $s=\frac{v^2}{2\mu g}=\frac{27.8^2}{2\cdot 0.5\cdot9.8}=78.7\ (m)$

(b) $s=\frac{v^2}{2\mu g}=\frac{27.8^2}{2\cdot 0.3\cdot9.8}=131.4\ (m)$