Question

A 2,000kg car uses a braking force of 12,000 N to stop in 5 s

Answer 1

Knowing the amount of force F and the length of time t that force is applied to an object will tell you the resulting change in its momentum ΔP . This is:

F*t = ΔP

ΔP = F*t    but ΔP = mv

mv = F*t

v = F*t/m

v = 12000 N × 5 s / 2000 kg

v = 30 m/s

A/ The initial speed of the car was 30 m/s