Question

Find the average frictional force needed to stop a car weighing 500 kg in a distance of 25 m if the initial speed is 72 km/h.

Answer 1

$m=500kg,S=25m,u=72km/h=20m/sec,v=0$

$(-a)=\frac{(v^2-u^2)}{2S}$

$\Rightarrow a=\frac{400}{50}=8m/se{c}^2$

Frictional force $f=ma=500\times 8=4000N$