Question

A car moving at 4 kmph is to be stopped by applying brakes in the next 40 m. If the car weighs 2000 kg, what average force must be applied on it?

Answer 1

According to the given question-

$u=4km/h$; initial velocity

$\Rightarrow u=\frac{10}{9}m{s}^{-1}$

$v=0m{s}^{-1}$; final velocity

$s=40m$; displacement

$m=200kg$; mass of the car

Using third equation of the motion:

$v^2-u^2=2as$

$\Rightarrow a=\frac{v^2-u^2}{2s}$

$\Rightarrow a=\frac{0-\frac{100}{81}}{2\times 40}$

$\Rightarrow a=-\frac{100}{80\times 81}m/s^2$

Now, apply the second law of newton

$F=ma$

$\Rightarrow F=-\frac{2000\times 100}{80\times 81}N$

$\Rightarrow F=30.86N$