Hydrostatic pressure forces and torque

1. Nov 9, 2009

Dr_bug

1. The problem statement, all variables and given/known data
Consider the dam in example 3. Suppose there is a rectangular gate near the top of the dam that can be used to release water. The gate is 4 m wide and 3 m tall and is hinged at its top edge so that it will close under its own weight. Determine the torque on the gate for rotation about its top edge when the water level is 8 m above its edge. see attachment for picture from example 3.

2. Relevant equations
Fℓ=(pgh)*(w dh)*(d-h)
w=sh +b
τ=∫[(pgh)*(sh +b)*(d-h)]dh-------going from 0 to d
3. The attempt at a solution
I'm having trouble getting started on this problem because i don't see how the gate fits into the picture. I'm not really understanding what they are asking. I would really appreciate any help at all... explanations of what I should do...

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Last edited: Nov 9, 2009
2. Nov 9, 2009

CJSGrailKnigh

Sorry if this doesn't help you but I think this question might be better placed in the engineering section. A fluid mechanics specialist would be able to help you out for this. I may just be tired but I believe this is beyond what I've covered so far in that subject.

3. Nov 9, 2009

Dr_bug

okay I'll try....its just that this is an intro physics course and i didn't think about putting it elsewhere

4. Nov 9, 2009

ideasrule

I don't think it's beyond introductory physics, and what the OP did is probably on the right track. Do you have a diagram though, Dr. bug? It's kinda confusing without one.

5. Nov 9, 2009

Dr_bug

oh yeah sorry i removed it when i reposted on the other page i'll put it back

6. Nov 9, 2009