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.

How much work each does? Take density of water = 10³ kg m^-3 and g = 9.8 N kg^-1.

Answer 1

Work done = mgh

Given,

density of water = 10³kg m ^-3

To convert, density of water to mass per litre

We know, 1 litre = 1000 cm³ and 1 m³ = 10⁶ cm³

So, `10^3 kgm^-3 = (1000 " kg")/(1 "m"^3)`

`= (1000 " kg")/(10^6 cm^3)`

`= (1  kg)/(1000  cm^3)`

`= (1  kg)/(1  litre)`

Hence, 20 L of water = 20 Kg by mass

height = 20 m

Now, substituting the values in the formula for work done we get

W = 20 × 9.8 × 20

W = 3.92 kJ