Question

A car moving with a speed of $40km/hr$ can be stopped by applying brakes after at least $2m$ If the same car is moving with a speed of $80km/hr$ what is the minimum stopping distance?

• A. $8m$
• B. $2m$
• C. $4m$
• D. $6m$

Answer 1

The correct option is A $8m$

Given,

$u=40km/h=\frac{40\times 1000}{60\times 60}=11.12m/s$

$v=0m/s$

$s=2m$

From 3rd equation of motion,

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

$a=\frac{v^2-u^2}{2s}=\frac{0^2-11.12\times 11.12}{2\times 2}$

$a=-30.86m/s^2$

Now, $u=80km/h=\frac{80\times 1000}{60\times 60}=22.22m/s$

$v=0m/s$

From 3rd equation of motion,

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

$s=\frac{v^2-u^2}{2a}=\frac{0^2-22.22\times 22.22}{-2\times 30.86}$

$s=8m$

The correct option is A.