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Question
A boy weighing 40 kgf climbs up a stair of 30 steps each 20 cm high in 4 minutes and a girl weighing 30 kgf does the same in 3 minutes. Compare:
- The work done by them.
- The power developed by them.
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Solution
(i) Weight of boy = Force = 40 kgf
Distance travelled in climbing 30 steps each
20 cm high = 30 × 20 = 600 cm = 6 m
Work done in 4 min = W = F × S
= 40 × 6 = 240
Weight of girl = Force = 30 kgf
Distance covered in 3 min = 6 m
∴ Work done in 3 min. = F × S
= 30 × 6
= 180 N
∴ Ratio of work done = 240 : 180 = 4 : 3
(ii) Power = `"W"/"T"`
Power developed by
Boy : Girl
⇒ `240/4 : 180/3`
⇒ 60 : 60
⇒ 1 : 1
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