Question

A person driving a car at the speed of $72\frac{km}{h}$ suddenly sees a boy crossing the road. If the distance moved by car, before the person applies brakes is $5m$, the reaction time of the person is:

• A. $0.5sec$
• B. $0.1sec$
• C. $10sec$
• D. $0.25sec$

Answer 1

The correct option is D

$0.25sec$

Step 1: Given data

Speed of car $=72\frac{km}{h}=72\times \frac{5}{18}=20\frac{m}{s}$

Distance covered$=5m$

Step 2: Formula used

Reaction time$\left(t\right)=\frac{dis\tan ce}{speed}$

Step 3: Solution

$$\begin{gathered} \Rightarrow t=\frac{5}{20} \\ \Rightarrow t=0.25sec \end{gathered}$$

Hence, the correct option is $D$.