Question

How much energy is gained by a box of mass 20 kg when a man

(a) carrying the box waits for 5 minutes for a bus?

(b) runs carrying the box with a speed of 3 m s-1 to catch the bus?

(c) Raises the box by 0.5 m in order to place it inside the bus? (g = 10 m s^-2)

Answer 1

Mass of box = 20 kg

(a) Zero work is done as there is no displacement of the man.

(b) Work done, Kinetic energy of man

(c) Work done in raising the box, Potential energy = mgh

U = 20 × 10 × 0.5 = 100 J