# Homework Help: I solved for the average force

1. Mar 2, 2006

### avb203796

A 50.0 kg person dives from a cliff above the water. From what height must he dive if he experiences an average force equal to 5.0 times his body weight (W=mg), as he comes to a stop in the water? You may assume a stopping time of 0.400 s.

So first I solved for the average force:

average F= 5.0(mg) = 5.0(9.80m/s^2)(50.0kg) = 2450N

Next I used the equation m*delta v = average F*delta t to solve for delta v:

delta v = [(2450)(0.4)]/50.kg = 19.6 m/s

I was wondering if my above calculations are right and then I am not sure how to now find the height using the delta v!

Last edited by a moderator: Jan 7, 2014
2. Mar 2, 2006

### physicsprasanna

ok .. now that you have found out delta v, you know the man's velocity as he reaches the water ... use the equations of motion to find the ht.

(you can use conservation of energy too)

3. Mar 2, 2006

### avb203796

Shouldn't my delta v be negative though because delta v = final velocity - intial velocity and my final velocity would be 0 because the diver is coming to a stop?

4. Mar 2, 2006

### topsquark

Check the signs on your vectors. That will explain it.

-Dan