Question

A car stops after $3s$ when brakes are applied. If the brakes offer a retardation of $5m{s}^{-2}$, what was the initial velocity of the car?

• A. $15m{s}^{-1}$
• B. $\frac{5}{3}m{s}^{-1}$
• C. $5m{s}^{-1}$
• D. $3m{s}^{-1}$

Answer 1

The correct option is A $15m{s}^{-1}$

Time, $t=3s$
Retadation, $a=5m/s^2$
Final velocity, $v=0$
Intial velocity, $=u$
So, $v=u-at$
$0=u-5\times 3$
$u=15m{s}^{-1}$