Question

An automobile moving at a speed of $72\text{km/h}$ is brought to rest in $2\text{s}$ by application of brakes. How much distance does the automobile cover in these $2\text{s}$?

• A. $\text{25 m}$
• B. $\text{20 m}$
• C. $\text{15 m}$
• D. $\text{10 m}$

Answer 1

The correct option is B $\text{20 m}$

Given:
$u=72\text{km/h}=72\times \frac{5}{18}=20\text{m/s}$
$v=0$
$t=2\text{s}$

Using,

$v=u+at$

$\Rightarrow 0=20+2a$

$\Rightarrow a=-10{\text{m/s}}^2$

Using,

$v^2=u^2+2as$

$\Rightarrow 0^2={20}^2+2\times (-10)\times s$

$\Rightarrow s=20\text{m}$

Hence, option $\left(B\right)$ is the correct answer.