Answer: - 70kN
Explanation: Since the car is moving westward that is to the left it's initial velocity Vi is -15 m/s. (Take note of the negative sign.)
It's final velocity Vf is 0 m/s since the car eventually came to rest. The time taken for this change in velocity is 0.3secs.
Recall that,
Acceleration
= change in velocity/time
= {Vf - Vi}/t
={0 - 15}/0.3
= - 50m/s²
Now force exerted on the car
F = mass* acceleration
= 1400kg*-50m/s²
= -70000N
= -70kiloNewton
