# Homework Help: Power of a water pump

1. Sep 5, 2011

### furor celtica

1. The problem statement, all variables and given/known data

A pump, taking water from a large reservoir, is used to spray a jet of water with speed 20 ms^1 and radius 0.05 metres, from a nozzle level with the surface of the reservoir. Calculate the power of the pump.

2. Relevant equations

3. The attempt at a solution

Alright I'll admit I'm pretty lost here and haven't been able to mount a very convincing attempt at a solution. I'm used to force-work-power problems based on the motion of an object so I'm not sure how to model this exercise. Even the wording is unclear; should I take initial speed 20 ms^-1, ending speed 0, distance 0.05? Where is the jet directed, horizontally or vertically?
Any suggestions would be appreciated.

2. Sep 5, 2011

### PeterO

In 1 second, you project a cylinder of water 20m long and 0.05m in diameter [thus calculate volume then mass of water] at 20m/s.
That mass of water will have kinetic energy - usual formula 0.5mv^2
So the pump has to supply that amount of kinetic energy per second.

In addition, potential energy may be involved - depends whether the water is ejected above or below the source.