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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-1.
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-1.
Class 10 | ICSE | Physics | Selina | Work Energy
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-1.

Solutions:

According to the question, both the people carry same weight of water to the same height but in different time periods.

(a)

(i) Since, both the people carry same weight of water to the same height, work done will be same for both.

Hence, Work = 1: 1

(ii) Power spent by both can be expressed in the following manner –

Pboy / Pfather = [(W / tboy) / (W / tfather)] = tfather / tboy

As the work done by both the persons is same.

∴ Pboy / Pfather = 2 / 3 = 2: 3

Thus, the ratio of the powers is 2:3

(b) Mass of water lifted by both can be determined using mass-density relation –

Therefore,

mw = p × V = 103 kg / m3 × 20 × 10-3 m3

= 20 kg

So, the work done becomes –

W = mwgh = 20 × 9.8 × 20

W = 3920 J

Or, W = 3.92 kJ

i

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