Question

A boy of mass 60 kg runs upstairs in 16 s and reaches 10 m high floor. Calculate:

1. Force of gravity acting on the boy.
2. Work done by the boy against the gravity.
3. Power developed by the boy.

Answer 1

Given: Mass (m) = 60 kg

Height (h) = 10 m

Time (t) = 16 s

Take acceleration due to gravity, g = 9.8 m/s².

(a) Force of gravity (weight) F = mg

= 60 × 9.8

= 588 N, acting downward.

(b) Work done against gravity (W) = mgh

= 60 × 9.8 × 10

= 5,880 J

(c) Power developed (P) = \[\frac{W}{t}\]

\[ = \frac{5{,}880}{16} \]

= 367.5 W