Question

A car moving with a speed of $50\text{km/hr}$, can be stopped by applying brakes after at least $6\text{m}$. If the same car is moving at a speed of $100\text{km/hr}$, the minimum stopping distance is

• A. $6\text{m}$
• B. $12\text{m}$
• C. $18\text{m}$
• D. $24\text{m}$

Answer 1

The correct option is D $24\text{m}$

By using third equation of motion
$v^2=u^2+2as$
Since the car is decelerating to zero velocity,
$0=u^2-2as$
$s=\frac{u^2}{2a}$
$s\propto u^2$
Hence, $\frac{s_2}{s_1}=\frac{u_2^2}{u_1^2}={\left(\frac{100}{50}\right)}^2$
$s_2=4s_1=4\times 6=24\text{m}$
Hence minimum stopping distance is $24\text{m}$