# Momentum - Jet of water

1. Feb 25, 2010

### ar202

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

A jet of water has a diameter of 30mm and a velocity of 40m/s. Determine the momentum/sec of the water. (Take p to be 10000kg/m3)

this is my first post, apologies if i have missed anything out...

2. Feb 25, 2010

### Stonebridge

Welcome to Physics Forums!

You need to show us some attempt at a solution, and tell us what exactly it is you don't understand, before we can help you?
Do you know the formula for momentum?

3. Feb 25, 2010

### ar202

Ah ok, to be honest i'm fairly lost. Most of the problems i've encountered so far have been to do with impact m1u1+m2u2=(m1+m1)v etc...

i'm not exactly looking for the answer, but perhaps a nod in the right direction :-)

4. Feb 25, 2010

### Stonebridge

If you think of the jet of water as a cylinder of water, what volume of water passes in one second? You have the radius/diameter of the end and you know how long the cylinder is from the speed of the jet.

5. Feb 25, 2010

### ar202

Yeah i thought of it that way but then hit a wall...

so the volume is pi*0.015^2*40 = 0.0283m^3 * 1000 = 28.3kg

then is it 28.3 * 40 to get 1132kgms-1 ? is there another step i'm missing?

6. Feb 25, 2010

### Stonebridge

That's it. That is the "mv" in one second.
Well done.

7. Feb 26, 2010