Question

In loading a truck, a man lifts boxes of 100 N each through a height of 1.5 m.
(a) How much work does he do in lifting one box?
(b) How much energy is transferred when one box is lifted?
(c) If the man lifts 4 boxes per minute, at what power is he working?
(g = 10 m s⁻²)

Answer 1

(a) While lifting the boxes to a height of 1.5 m, the work is done by the man against the gravitational pull of the earth.

Work done against the gravity is given by, $W=mgh$. (Where 'm' is the mass of the body, 'g' is the acceleration due to gravity and 'h' is height up to which the body is taken)

In the given case, weight of one box = mg = 100 N

Height up to which the man lift the box = 1.5 m

Work done by the man = mgh = 100 N $\times$ 1.5 m= 150 J

(b) The work done by the man is stored in the box as the potential energy of the box by virtue of its height with respect to ground. So, when one box is lifted the total work done of 150 J is transfered to the box in form of energy.