Question

A car of mass 2000 kg is lifted up a distance of 30 m by a crane A in 1 minute as

shown in the figure given below. The second crane B does the same job in 2

minutes. (g = 9.8 m/s2

)

4

1. Work done by the

(a) crane A is more than that of B

(b) crane A is less than that of B

(c) crane A is equal to that of B

(d) none of the above

2. Power supplied by crane A is

(a) 9.8 kW (b) 19.6 kW

(c) 26.8 kW (d) 99.4 kW

3. Power supplied by crane B is

(a) 1.8 kW (b) 4.9 kW

(c) 16.4 kW (d) 29.6 kW

4. If the efficiency of crane A is 55%, its input power is

(a) 7.81 kW (b) 9.46 kW (c) 17.82 kW (d) 72.85 kW​

Answer 1

Explanation:

1. (c)

2. (a)

Power = work/time = (2000×9.8×30)/60= 9.8kW

3. (b)

Power = work/time =(2000×9.8×30)/120= 4.9kW

4.(c)

55% efficiency, it means

55% of total input power = output power

= 9.8kW

Total input power = (9.8kW × 100)/55 = 17.81kW