Question

A driver has to apply sudden brakes to stop his vehicle moving at $72km/hr$ and stops within $2seconds$. The retardation produced is then

• A. $20m/s^2$
• B. $10m/s^2$
• C. $15m/s^2$
• D. $18m/s^2$

Answer 1

The correct option is B $10m/s^2$

Using the first equation of motion, $v=u+at$
Here, $v=0$
$u=72\times \frac{1000}{3600}=20m/s$
$t=2s$

Hence, $0=20+a\times 2$

$a=-\frac{20}{2}=-10m/s^2$

Since, sign of $a$ is negative. Hence, retardation with magnitude $10m/s^2$ is produced.