Question

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

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

Answer 1

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

The minimum stopping distance is achieved by constant braking at maximum strength. So, assuming a constant acceleration of - $a_b{\text{m/s}}^2$ because of braking:
For stopping, $v=0$ at the end of braking,
$\to v^2=u^2+2as$
$\to 0^2=u^2-2a_{b}s$
$\to u^2=2a_{b}s$
$\to s\alpha u^2$
$\to \frac{s}{6}=(\frac{100}{50}{)}^2$
$\to s=24\text{m}$