Find the average force needed to accelerate a car weighing 500 kg from rest to 72 km/h in a distance of 25 m.
Initially the car is at rest, the speed of the car = 0 m/s
We need to accelerate the car to a speed of = 72km/h = 20 m/s
Kinetic energy at this speed = (1/2) ×500×20×20 = 105 J
The change in kinetic energy = 105 m/s
The work done in this process = change in kinetic energy
= 105-0 = 105 J
Also, we know that work done = force × displacement
⇒ Force = work done/ displacement = 100000/25 = 4000 N