Question

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

• A. $24m$
• B. $22m$
• C. $20m$
• D. $8m$

Answer 1

The correct option is A $24m$

Speed of the car when stopping distance is $6m$ is given as, $u_1=50\frac{km}{hr}$
And let say $u_2=100\frac{km}{hr}$
Now,
$v^2=u^2-2as\Rightarrow 0=u^2-2as\Rightarrow s=\frac{u^2}{2a}\Rightarrow s\propto u^2$
($a$ is constant and negative as considering retardation)

$\therefore \frac{s_2}{s_1}=\frac{u_2^2}{u_1^2}=\frac{{100}^2}{{50}^2}\Rightarrow s_2=4s_1=4\times 6=24m$