Question

Calculate the horse power of the motor of an elevator, which can carry 10 persons of average mass 60 kg through a vertical height of 20 m in 30 s.

[Take g = 10 N/kg, 1 HP = 750 W]

Answer 1

Total mass of the 10 persons = 10 × 60 = 600 kg

Work done in lifting them = mgh

= 600 × 10 × 20

= 120000 J

\[ \text{Power} = \frac{\text{Work}}{\text{Time}} \]

\[= \frac{120000\ \mathrm{J}}{30\ \mathrm{s}} \]

= 4,000 W

Power in HP = `4000/750`

= 5.33 HP