Question

16. 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-and
g= 9.8 N kg-​

Answer 1

Answer:

Volume of water = 20 l = 20/1000= 0.02 m^3

Mass of water = Density × Volume = 10^3×0.02 = 20 kg

(i) Work done by boy = mgh = 20×9.8×20 = 3920J

Work done by father = mgh = 20×9.8×20=3920J

Compare work done =>

3920 : 3920

= 1:1

(ii) Time taken by boy = 3 min = 180 s

Time taken by father = 2 min = 120 s

Power developed by the boy = Work done /Time = 3920/180

Power developed by the father = Work done /Time = 3920/120

Comparing power devolped =>

3920/180 : 3920/120

=2:3