# Avereage Net Force

1. Oct 14, 2008

### Naldo6

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

A 76.0 kg diver falls from rest into a swimming pool from a height of 6.9 m. It takes 1.44 s for the diver to stop after entering the water. Find the magnitude of the average net force exerted on the diver during that time.

2. Oct 14, 2008

### BishopUser

What equations do you know of that would be relevant to this problem? Where are you getting stuck at in trying to solve this problem?

3. Oct 14, 2008

### Naldo6

idont know how to do it.. i just know that F= J/delta t...but i dont know anymore ...or i dont know if this proble is solved by other way or other formula....

4. Oct 14, 2008

### aimslin22

wouldn't the only force be gravity?

5. Oct 14, 2008

### Naldo6

i dont know... byt F= J/delta t
and J=delta P= (mass)( velocity - 0)
and i dont know if the 1.44 s is the right delta t to the formula...

also i need to calculate that velocity because the mass is 76.0 kg

6. Oct 14, 2008

### aimslin22

After rereading the problem, wouldn't you need to find the bouyent force and then subtract the mg from it? Because those are the only two force I see working on the diver.

7. Oct 14, 2008

### Naldo6

and how i do that?... plz explian me better....

8. Oct 14, 2008

### aimslin22

sorry, I don't remember the formula, but there is another way I think.

It's rather long.

You know the formula F=ma right?

The diver has an upward force pushing it up until it stops and a downward force.
The downward force is mg. To find the upward force:

upwardforce - mg = ma

because the mg is smaller (that's why it stops) we the upward force (winner) from the downwardforce (loser)

but you don't know a, but you could find it.

first, figure out the final velocity of the diver RIGHT BEFORE he hits the water. This can be found by using a distance formula. Vf^2 = Vi^2 + 2ad.

That final velocity becomes the intial velocity once the diver is in the water. So use another formula, Vf = Vi + at, and solve for a.

Finally, go back to the top and plug in a.

*The net force should be the upward force - the downward force* because net force is by how much a force is winning

I hope this right. I am not too sure, but this looks like the best way to solve the problem.

9. Oct 14, 2008

### Naldo6

thanks i did it...