Need help obtaining hydrostatic forces on a gate

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1. Apr 28, 2015

lvluffinz

I know we need to use F = pgA(h bar), as that's what I'm given in notes and whatnot, but I can't for the life of me get this simple one done.

Any help would be GREATLY appreciated as I have an exam coming up on this.

Last edited by a moderator: Apr 28, 2015
2. Apr 28, 2015

Staff: Mentor

It is not that simple. Two questions that might help:
What is the water pressure at the horizontal part?
What is the difference between "does not move yet" and "starts to move", which condition has to be satisfied to not move?

3. Apr 28, 2015

lvluffinz

We weren't given any of that info. Just threw this question on us...

4. Apr 28, 2015

Staff: Mentor

This is something you should find out! The given information is sufficient to do so.
You'll also need the density of water and the gravitational acceleration g but those are well-known values.

5. Apr 28, 2015

lvluffinz

He's basically disappeared until the exam, so there isn't a thing I could do sadly.

6. Apr 28, 2015

Staff: Mentor

You can use the hints that you've been given in the thread and the hints I sent you via PM to draw the FBD and start working out the forces and moments. We require that you show effort on your schoolwork here before we can offer tutorial help...

7. Apr 28, 2015

lvluffinz

Doing that right now!

8. Apr 28, 2015

haruspex

I'm not sure I understand the diagram. I think the gate is an L shape, but the gap between the hinge and the vertical part bothers me.

9. Apr 28, 2015

Staff: Mentor

Yeah, I think it's drawn incorrectly as well. I mentioned that to the OP in a private conversation we were having, and I probably should have posted it in-thread as well.

10. Apr 29, 2015

lvluffinz

Should have updated this thread, but I've figured it out. Solved it and all! I'll post the answer later tomorrow as I'm about to head to bed for my exam!

EDIT: I just scanned my working pretty quick and snipped it. will post here.

Last edited by a moderator: Apr 29, 2015
11. Apr 29, 2015

haruspex

I get the same.