A boy weighing 40 kgf climbs up a stair of 30 steps each 20 cm high in 4 minute and a girl weighing 30 kgf does the same in 3 minutes. Compare :-

(i) The work done by them.

(ii) The power developed by them.

(i) The work done by them = ?

While climbing both the girl and boy have to do work against the force of gravity.

Force of gravity on boy = F₁ = m₁g = 40 x 10 = 400

Force of gravity on girl = F₂ = m₂g = 30 x 10 = 300

Total height climbed up

h = number of steps x height of each step

= 30 x 20 = 600 cm = 6 m

Work done by the boy = W₁ = F₁ x h = 400 x 6 = 2400 J

Work done by the girl = W₂ = F₂ x h = 300 x 6 = 1800 J

Therefore, W₁ : W₂ = 2400 : 1800 = 4 : 3

(ii) The power developed by them = ?

$\dfrac{P$1}{P2} = \dfrac{\dfrac{W1}{t1}}{{\dfrac{W2}{t2}}} \\[0.5em] = \dfrac{W1}{W2} \times \dfrac{t2}{t1} \\[0.5em] = \dfrac{4}{3} \times \dfrac{3}{4} \\[0.5em] = 1 : 1