Question

20 litre water per second is lifted from well 45m and delivered with a velocity of 10m/s, then the power of motor is

Answer 1

i)

Lifting of water above ground = m * g * h

= 20 kg * 10 m/s² * 45 m

= 9000 W or 9 kW

ii)

Kinetic Energy = 1/2 * m * v²

= 1/2 * 20 * 10 * 10

= 1000 W or 1 kW

Answer: 9 kW + 1 kW = 10 kW

Answer 2

10kW

Explanation:

20 l of water means 20kg

because density = m/vol.

and density=1

so, if vol. = 20 l = 20 m^3

then m=20kg

before lifting :

P.E.=mgh

=20×10×45

=9000J

and

after lifting:

K.E.=1/2 m(v)^2

=(20×(10)^2)÷2

=2000÷2

=1000J

so, T.E.=Work done =9000J+1000J

=10000J

and power =Work /time

=10000J/1s

=10000W

=10kW