Question

81. A 2.0 hp motor pumps out water from a well of
depth 8 m and fills a water tank of volume 1492
litres at a height of 16 m from the ground. The
running time of the motor to fill the empty water
tank is:: (g = 10m/s2)
(1) 50 minutes
(2) 10 minutes
(3) 4 minutes
(4) 20 minutes
​

Answer 1

Answer:

3) 4 minutes is answer dear friend

Answer 2

Answer:

☆Concept:

》the water is being lifted from the ground to some height, for that the motor has to overcome its potential energy(PE) to lift it

》in the ques the area of the inlet pipes are not given,so here we are assuming that at height ,its PE is ultimately give its velocity to fill the tank,

we do not have to provide the extra velocity to get fill the tank.

☆Given:

》Power = 2 hp = 2 × 746 (1HP=746watts)

》Power = (2×746)W

》height (see the attachment !)

height(total) = below the ground + above the ground

》height = 8 + 16

》height = 24m

》mass = density × volume(density of water)

mass = 1kg/litre × 1492litres

》mass = 1492 kg.

☆Solution:

》power = $\dfrac{work\;against\;PE}{time}$

》2×746 = $\dfrac{mgh}{t}$

》2×746 = $\dfrac{1492×10×24}{t}$

》time = $\dfrac{1492×10×24}{2×746}$

》time = 240 sec = (240/60)mins

》time = 4mins.

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♧hope it helps! ♧