Question

By applying brakes, a car moving at $1m{s}^{-1}$ is brought to rest in 3 s. If it moves at $2m{s}^{-1}$, how long will it take to come to rest?

• A. $6s$
• B. $12s$
• C. $3s$
• D. $1s$

Answer 1

The correct option is A $6s$

$u=1m{s}^{-1}$
$v=0$
$t=3s$
$\therefore$ Retardation, $a=\frac{u-v}{t}=\frac{1-0}{3}m{s}^{-2}=\frac{1}{3}m{s}^{-2}$
Now, $u=2m{s}^{-1}$$,v=0,a=-\frac{1}{3}m{s}^{-2}$
Let the time be $t$.
$v=u+at$
$0=2-\frac{1}{3}t$
$t=6s$