The mass of a vehicle of 5 tons is moving at a speed of 72 km / h. What work must be done to stop it?

Data: m (vehicle weight) = 5 t; V1 (the speed at which the car is moving) = 72 km / h; V2 (final speed, vehicle must stop) = 0 m / s.

SI system: m = 5 t = 5 * 10 ^ 3 kg; V = 72 km / h = 20 m / s.

According to the theorem about the change in kinetic energy, the work that must be done to stop the car: A = Ek1 – Ek2 = 0.5 * m * V1 ^ 2 – 0.5 * m * V2 ^ 2 = 0.5 * m * V1 ^ 2.

Calculation: A = 0.5 * 5 * 10 ^ 3 * 20 ^ 2 = 1000 * 10 ^ 3 J or 1 MJ.

Answer: 1 MJ work must be done.