# Another Hydrostaic force Problem

1. Dec 20, 2009

This is a problem right out of the text of my calculus book. So I actually have the work, but I'm confused about something the did.

Problem: Find the hydrostatic force on one end of a cylindrical drum with radius 3 ft. if the drum is submerged in water 10 ft deep.

I attached a diagram

Pressure can be defined:

p=density, d=distance below the surface

$$P=pgd=\delta d$$

The area of the ith strip is:

$$A_i=2\sqrt{9-(y^*_i)^2}\Delta y$$

The average distance below the surface is:

$$d_i=7-y^*_i$$

Then when they write the pressure, they give:

$$\delta_i=62.5(7-y^*_i)$$

The implies that $$pg=62.5$$.

The density of water is $$p=62.4 lb/ft^3$$

http://en.wikipedia.org/wiki/Density_of_water

Gravitational acceleration is $$32.174 ft/s^2$$

So how does $$\delta d_i=pgd_i=62.5(7-y^*_i)$$ ? Is this an error? It seems that they accidently neglected to account for gravitational acceleration.

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2. Dec 20, 2009

### ideasrule

Yeah, it's an error.