# hydrostatic force

• Dec 8th 2008, 07:01 PM
woooo
hydrostatic force
Can anyone help me with this word problem ? -__-

1.
A dam is inclined at an angle of 30± from the vertical and has the shape of an isoceles trapezoid 100 ft wide at the top and 50 ft wide at the bottom and with a slant height of 70 ft. Find the hydrostatic force on the dam when it is full of water.

Thanks!
• Dec 8th 2008, 08:33 PM
woooo
nevermind i got the answer yay!!
• Dec 9th 2008, 03:56 PM
christinaaa
Whoa I got this same problem.. How do you do it?
• Dec 9th 2008, 04:17 PM
galactus
Since it is 30 degrees to the vertical, then we can use sin(60), which I will represent in radians.

$\displaystyle 62.4\int_{0}^{70}(xsin(\frac{\pi}{3}))(100)dx$
• Dec 9th 2008, 05:01 PM
christinaaa

I think mostly I'm having trouble drawing the picture, so I can't really get any farther than that. Would you mind redrawing with the given information?

Thanks!
• Dec 9th 2008, 06:54 PM
woooo
christinaaa, r u also in pham's class ? lol

for finding height of dam = sqrt((70)^2 - (25)^2) cos30

then for width of trapezoid = 100-x/h (100-50)

then u take the integral of the width which u got from above, from 0 to h
• Dec 9th 2008, 08:24 PM
christinaaa
Do you have a picture?

Isn't the formula for hydrostatic force something like F = the integral of 1000 x 9.8 x area of the dam, from 0 to h?