Question

An engine pumps water through a hose pipe. Water
passes through the pipe and leaves it with a velocity
of 2 m/s. The mass per unit length of water in the
pipe is 100 kg/m. What is the power of the engine?
[AIPMT (Prelims)-2010]
(1) 300 W
(2) 400 W
(3) 200 W
(4) 100 W
answer is 300 .how?????​

Answer 1

Answer:

Explanation:

The water from the hose pipe comes out at the speed, v = 2 m/s

Mass per unit length of the pipe = 100 kg/m

So, amount of water that comes out per second = 100 × 2 = 200 kg (since, the water covers 2 m per second and there is 100 kg water per meter)

Therefore, Kinetic energy of the water coming out per second is KE = ½ × 200 × 22 = 400 J

This is also the work done by the pump per second. So, the power of the pump is, P = 400/1 = 400 W