Answer: Option A
:
A
For calculating force, we need to calculate deceleration first. From thethird equation of motion,
$v^2-u^2=2aS$ where, v- final velocity, u- initial velocity, a- acceleration and S- distance travelled.
Given, u=$20m{s}^{-1}$, S$=50m$, mass $m=1000kg$ and v$=0$.
Therefore, $0-{20}^2=2\times a\times 50$
$\Rightarrow a=-4m{s}^{-2}$
Let the force acting on the car be $F$.
From Newton's second law,
$F=ma$
$\Rightarrow F=1000\times (-4)=-4000\text{N}$
Hence, the net force is$-4,000N$. The negative sign indicates that the force is acting opposite to the direction of initial velocity and causes deceleration. This net force is actually the frictional force acting between the ground and the tyre of the car.