# Homework Help: What is the cross section area of the water?

1. May 3, 2012

### yy205001

what is the cross section area of the water??

1. The problem statement, all variables and given/known data
Determine an expression for the cross sectional area A of the fluid in the tank as a function of D and H.

2. Relevant equations
A=pi*r2

3. The attempt at a solution
i try to let the radius equal to the height but then the fluid's height goes lower, it doesn't form a circle anymore. So i have no ideas how to do this.Please help.

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2. May 3, 2012

### Staff: Mentor

Re: what is the cross section area of the water??

What is the shape of the tank? In your drawing, the cross-section is half a circle, but is the tank spherical or cylindrical or what? To get an expression for the cross-sectional area of the water, you need to know the shape of the tank.

3. May 3, 2012

### sharks

Re: what is the cross section area of the water??

I believe the tank is a half sphere? So, the volume of the sphere is: $$\frac{2}{3}\pi r^3$$

4. May 3, 2012

### Staff: Mentor

Re: what is the cross section area of the water??

Nothing in the OP's post says anything about the actual shape of the tank.

5. May 3, 2012

### sharks

Re: what is the cross section area of the water??

If you click on the attached picture in the first post, it does say "hemispherical" in the lower-right corner. In that case, H= r (radius if sphere) and D = 2r (diameter).

6. May 3, 2012

### Staff: Mentor

Re: what is the cross section area of the water??

So it does. I missed that.