Question

A boy of mass 55 kg runs up a flight of 40 stairs, each measuring 0.15 m in 15 s. Calculate

1. Force acting on the boy.
2. Work done by the boy.
3. Gain of potential energy by the boy.
4. Power developed by the boy.
5. Horse power and power in kilowatts.

Answer 1

(a) Force = mg = 55 kg × 10 m s⁻² = 550 N

(b) Work = F × S = 550 N × (40 × 0.15) m = 3300 J

(c) PE = Total work done = 3300 J

(d) \[ \text{Power} = \frac{W}{t} = \frac{3300\ \mathrm{J}}{15\ \mathrm{s}} = 220\ \mathrm{W}\]

(e) \[ \text{Power in HP} = \frac{220}{750} = 0.29\ \mathrm{HP}\]

\[ \text{Power in kW} = \frac{220}{1000} = 0.22\ \mathrm{kW}\]