Fluid mechanics problem, need explanation please

  • Thread starter Bassel
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  • #1
Bassel
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Hi please check the highlighted question in the attachment and the solution and see the problem, i need help please. I have two questions about it:

1- why didn't we take the plug as a vertical wall and thus the force would be integral of pressure x area?

2-WHERE DID THE FORCE DUE TO ATMOSPHERIC PRESSURE GO?

Thnx for your help.
 

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Answers and Replies

  • #2
tiny-tim
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Hi Bassel! Welcome to PF! :smile:
1- why didn't we take the plug as a vertical wall and thus the force would be integral of pressure x area?

You did.

You did ∫ ρgA(H+h) dh, but the plug is so small that you can take H+h to be a constant, H …

so that integral is just ∫ ρgAH dh :wink:
2-WHERE DID THE FORCE DUE TO ATMOSPHERIC PRESSURE GO?

it nipped round the other side when you weren't looking, and started pushing back :smile:

(so it's the same on both sides, and you can ignore it)
 
  • #3
Bassel
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by the other side you mean from outside ??
 
  • #4
tiny-tim
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yes, the plug has two sides :smile:
 

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