5. A boy takes 3 minutes to lift a 20 litre water bucket from a 20 m deep well, while his father does it in 2 minutes. (a) Compare : (i) the work, and (ii) power developed by them. (b) How much work each does ? Take density of water = 103 kg m-3 and g = 9.8 N kg-
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Answer:
Density of water =1000kg/m
3
=1kg/liter
Mas of 20 liter water =20kg=m
(a)(i)Work done in both cases =mgh
=20×9.8×20=400×9.8=3920J
(ii)Power developed in case1: =
timetaken
workdone
=
3×60
3920
=21.78W
Power developed in case2: =
timetaken.
workdone
= 2×60
3920 =32.67W
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