Question

A constant retarding force of $50$ $N$ is applied to a body of mass $20$ $kg$ moving initially with a speed of $15$ $m{s}^{-1}$. How long does the body take to stop?

Answer 1

Retarding force, $F=50N$

Mass of the body, $m=20kg$

Initial velocity of the body, $u=15m/s$

Final velocity of the body, $v=0$

Using Newtons second law of motion, the acceleration ($a$) produced is given by:

$F=ma$

$50=20$ $\times a$
$a=-50/20=-2.5m/s$${}^2$

Using the first equation of motion, the time ($t$) taken by the body to come at rest

$v=u+at$

$t=-u/a=-15/-2.5=6s$