Hydrostatic Force (Out of my Calc book)

mateomy
Messages
305
Reaction score
0
This is technically a physics problem but its straight outta my calculus book...

water.jpg


The instructions are to express the force as an integral and evaluate it.


My problem is just the initial set up. I've tried a couple of different ways and none of them get me the answer that I am seeing in the back of the book.


I know that I am looking at a half circle so that would be \frac{1}{2}\pi(r^2) and I would be evaluating it with respect to x (or y, depending on my axes). Also, the semicircle is submerged 2ft below the surface, so is that (total depth - y), (7 - y)? I am super confused.

On top of all this, I don't even know what upper and lower bounds I should be evaluating it at. 2 to 7? 0 to 5?

All in all this is the closest -yet, incorrect- way I've come to setting it up. Oh, I am using \delta as my weight density (62.5 lb/ft^3).

<br /> \int\limits_?^? \delta \frac{\pi}{2} (\sqrt{r^2 - y^2})^2 (7 - y) dy<br />

Completely lost, any help or nudges in the right direction would be tremendously appreciated.
 
Physics news on Phys.org
Never mind...got it.
 
There are two things I don't understand about this problem. First, when finding the nth root of a number, there should in theory be n solutions. However, the formula produces n+1 roots. Here is how. The first root is simply ##\left(r\right)^{\left(\frac{1}{n}\right)}##. Then you multiply this first root by n additional expressions given by the formula, as you go through k=0,1,...n-1. So you end up with n+1 roots, which cannot be correct. Let me illustrate what I mean. For this...
Back
Top