Question

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 = 10³kg m^-3 and g = 9.8 N kg^-1

April 17, 2024

Answer

(a) (i) Work done = force × displacement

Work done is same for boy and father as both lift 20 litre water from 20 m deep well.

Work done by boy : Work done by father = 1:1

(ii) Comparing Power developed:

Power of boy : Power of father = $W\over 3$ : $W\over 2$

= $2\over 3$

Power developed by boy : Power developed by father = 2:3

(b) Work done = mgh

= 20 × 9.8 × 20 [20 lt water = 20 kg water]

= 3920 J

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