Pressure and Net Force Question

  • Thread starter Enoch
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I'm working on my homework, and I have finished all the problems save for one. I think I am on the right track, but I'm lacking just a few bits of info. Here is the question (it has 2 parts, I have answered the first part correctly, but cannot get the second part correct).

Part 1

Engineers have developed a bathyscaph that can reach ocean depths of 7.72 mi. The acceleration of gravity is 9.8 m/s^2. If the density of seawater is about 1030 kg/m^3, what is the absolute pressure at that depth in Pa?

Answer - P = Pinitial + pgh = 1.25484 x 10 ^8

Part 2 (here is where I need help)

If the inside of the vessel is maintained at atmospheric pressure, 101300 Pa, what is the net force on a porthold of diameter 20.9 cm? Answer in units of N.

Well I know that F = PA, so I set up the equation:

PA - Pinitial(A) = density(g)(h)(A)

However, this doesn't solve for net force. I'm not sure if this is the actual equation I need, or if I can use it to find the net force. I was under the impression that PA - Pinitial(A) would equal the net force but it does not. I assume that I need the 20.9 cm in there somewhere. Any help is appreciated.
 

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