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Question

a boy of mass 40 kg runs up a flight of 50 steps , each of 10 cm high, in 5 sec. find the power developed by the boy ?

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Solution

Dear Student

Mass of the boy (m1) = 40 kg
Mass of the girl (m2) = 50 kg
Time taken by boy (t1) = 50 sec
Time taken by girls (t2) = 40 sec
Height of each stair = 0.15 m
acceleration due to gravity = 10 m/s2
Number of steps = 50
Total height moved by him (h) = 50 x 0.15 m = 7.5 m
(a) Work done by Boy in moving against gravitational pull (W1) = m1gh = 40 x 10 x 7.5= 3000 J
Work done by girls in moving against the gravitational pull (W2) = m2gh = 50 x 10 x 7.5 = 3750 J
Ratio of W1 and W2 = W1W2 = 30003750 = 0.8
(b) Power developed by boy = Workdone Time =300050 =60 Power developed by girls =WorkdoneTime =375040 =93.75Ratio of Power developed = Power developed by boyPower developed by girls =6093.75 =0.64

Regards

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