Question

A boy of mass 50 kg climbs up the stairs and reaches the roof at a height of 10 m in 20 s. Calculate (i) the force of gravity acting on the boy, (ii) the work done by him against the force of gravity and (iii) the power spent by the boy. (Consider g = 10 ms⁻².)

Answer 1

Given Data:

Mass of the boy (m) = 50 kg

Height climbed (h) = 10m

Time taken (t) = 20 s

Acceleration due to gravity (g) = 10 m/s²

(i) The force of gravity acting on a body is equal to its weight.

F = m × g

= 50 kg × 10 m/s²

= 500 N

(ii) The work done in climbing up against gravity is stored as gravitational potential energy.

W = m × g × h

= 50 kg × 10 m/s² × 10 m

= 5000 J

(iii) Power is defined as the rate of doing work.

P = `W/t`

= `(5000  J)/(20  s)`

= 250 W