Question

A car moving with a speed of 40 km/h can be stopped by applying brakes after at least 2 m. If the same car is moving with a speed of 80 km/h, what is the minimum stopping distance?

Answer 1

Initial velocity, $u=40km/h=40\times \frac{5}{18}=\frac{200}{18}m/s$

Final velocity, $v=0$

Distance travelled before coming to rest, $s=2m$

Using the equation, $v^2=u^2+2as$

$⟹a=\frac{-u^2}{2s}$

$⟹a=-30.864m/s^2$

Again,

$u=80km/h=\frac{400}{18}m/s$

$v=0$

$a=-30.864m/s^2$

Now, $v^2=u^2+2as$

$⟹s=\frac{-u^2}{2a}=8m$