Question

3. A boy of mass 40 kg climbs up a flight of 30 steps
each 20 cm high in 2 min and a girl of mass
30 kg does the same in 1.5 min. Compare : (i) the
work done, and (ii) the power developed by them
(g = 10 m s-2)​

Answer 1

Given : a boy of mass 40 kg climbs 30 steps  each   20 cm high in 2 minutes and a girl of mass  30 kg does the same in 1.5 min.

To Find : (i) the  work done, and (ii) the power developed by them

Solution:

Step height = 20 cm

Number of steps = 30

Total height raised = 30 * 20  = 600 cm

100 cm = 1 m

=> Total height raised = 6 m

Work done = Increase in potential energy  = mg ( height increased)

Boy

m = 40 kg

g = 10 m/s²

h = 6m

Work done =   40 * 10 * 6

= 2400 jule

=> Work done by boy = 2400 joule

girl m = 30 kg

Work done by girl  =30*10 * 6 =  1800 joule

Word done by boy > Work done by girl

Power = Word done/ Time

=> Power developed by boy =   2400 / 120  = 20 W

=> Power developed by girl = 1800/90 = 20W

Power developed by both are equal .

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