Question

A vehicle moving with speed $30km/h$ on a straight road can be stopped in $6m$ distance by applying brakes. If same vehicle is moving with $60km/h$ and brakes provide double retardation then vehicle will stop after travelling :

• A. $6m$
• B. $12m$
• C. $18m$
• D. $24m$

Answer 1

Answer: (B)

$12m$

Given,

$u=30km/h=\frac{25}{3}=8.333m/s$

$S=6m$

$v=0m/s$

The 3rd equation of motion,

$2aS=v^2-u^2$

$a=-\frac{8.333\times 8.333}{2\times 6}=-5.787m/s^2$

Now,

$u=60km/h=\frac{50}{3}=16.666m/s$

$a=-11.574m/s^2$

$v=0m/s$

From 3rd equation of motion,

$2as=v^2-u^2$

$s=-\frac{u^2}{2a}$

$s=\frac{16.666\times 16.66}{2\times 11.57}$

$s=12m$

The correct option is B.