Question

Calculate the height through which a crane can lift a load of 4 t, when its motor of 4 HP operates for 10 s.

(Take g = 10 ms⁻², 1 HP = 750 W)

Answer 1

Mass of the load = 4 t = 4000 kg

Power of the motor = 4 × 750 = 3000 W

Work done in 10 s = Power × Time

= 3000 × 10

= 30000 J

Since work done in lifting the load = mgh

30,000 = 4,000 × 10 × h

30,000 = 40,000 × h

\[ \therefore\ h = \frac{30{,}000}{40{,}000} \]

= 0.75 m