# Homework Help: How could spring water lift a person?

1. Aug 27, 2006

### scalar

In an TV advertisement, a young man was lifted by an artificial spring water to a hight about 4 m. Supposed the man's weight is 800N, and the sectional area of the spring water is 0.2*0.2 m^2, and using the impuse-momentum theorem, I got a velocity of the spring water of 4m/s.
Is this correct?

Last edited: Aug 28, 2006
2. Aug 28, 2006

### DaveC426913

As long as the water table of the spring at its source was more than 4m above the ground where the man was standing, you're good to go, and you don't need all those fancy calculations.

3. Aug 28, 2006

### Andrew Mason

I don't quite understand what Dave is saying.

I get 4.5 m/sec at the height where the man is located. $F = vdm/dt = v\rho dV/dt = v\rho Av = \rho Av^2$. What is the velocity at the ground level?

AM

4. Aug 28, 2006

### DaveC426913

I was second-guessing him. I was assuming he wanted to figure out whether it was practically possible for a volume of water to lift a man 4 metres, (after all, that's what his thread title implies he's asking about), but that his method for doing so was with numbers (calcing the speed and momentum of the water) rather than deduction.

I was merely pointing out that, if the (inexhaustible) supply of the spring water was higher than ground (i.e. at least 4m higher) where the man is standing, then is is trivial to show that the water will shoot that high.

Last edited: Aug 28, 2006
5. Aug 29, 2006

### scalar

aha, just as dave said, I'm discussing the posibility of the advertisement. And the method I used is the same as Andrew's. The velocity of the spring water at the ground is about 10m/s. Thank you all.

Last edited: Aug 29, 2006