Question

A vehicle moving at $36km/hr$ is to be stopped by applying brakes in the next $5m$. If the vehicle weighs $2000kg,$ determine the average force that must be applied on it

• A. $10^{4}N$
• B. $2\times 10^{4}N$
• C. $3\times 10^{4}N$
• D. $5\times 10^{3}N$
• E. $10^{3}N$

Answer 1

Answer: (B)

Given, initial velocity of vehicle $u=36km/h$
$=10m/s$
Stopping distance of vehicle $s=5m$ and
mass of vehicle $m=2000kg$
So, from equation of motion
$v^2-u^2=2as$
since, final velocity of vehicle $v=0$ and acceleration of vehicle $=-a$ (acceleration)
$\Rightarrow -u^2=-2as$
$\Rightarrow a=\frac{u^2}{2s}$
$=\frac{10\times 10}{2\times 5}=10m/s^2$
The average force for braking
$F=ma=2000\times 10=2\times 10^{4}N$