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 = 103 kg m-3 and
g = 9.8 N kg-​

Answer 1

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

(b)Each does work =mgh=3920J