Evacuatred chamber pressure question

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SUMMARY

The discussion centers on calculating the force required to remove a circular cover from an evacuated chamber with a pressure of 22.5 kPa. The user initially attempted to apply the principle of pressure and area (F1/A1=F2/A2) but arrived at inconsistent results, including forces of 113.1N, 481N, and 1510N. Key insights reveal the necessity of considering three forces: atmospheric pressure acting down on the cover, chamber pressure acting up, and the user's pulling force. A more accurate approach involves careful analysis of the free body diagram to isolate the pulling force.

PREREQUISITES
  • Understanding of basic physics principles, specifically pressure and force calculations.
  • Familiarity with free body diagrams and their application in force analysis.
  • Knowledge of atmospheric pressure effects on objects.
  • Basic mathematical skills for solving equations involving area and pressure.
NEXT STEPS
  • Study the principles of fluid mechanics, focusing on pressure differentials.
  • Learn to construct and analyze free body diagrams for complex systems.
  • Explore the effects of atmospheric pressure on various shapes and sizes of covers.
  • Investigate real-world applications of evacuated chambers in engineering.
USEFUL FOR

This discussion is beneficial for physics students, engineers, and anyone involved in mechanical design or pressure-related applications, particularly those working with evacuated systems.

Kristin
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I've been working on this question for quite a while and I've tried several methods with no success. I am no where near confident in my method and I was wondering if someone could point me in the right direction. The question is:

A 16.5 cm diameter circular cover is placed over a 8.0 cm diameter hole that leads into an evacuated chamer. The pressure in the chamber is 22.5 kPa. How much force is required to pull the cover off?

I attempted to solve by using F1/A1=F2/A2
so... I got F1=P1A1
=113.1N

And 113.1N/5.027e-3m=x/2.138e-2m
Isolating for x, and then F2=481N
I have also tried other methods and gotten F2= 1510N, 156N, 1511N, 212N, and 665N.
 
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You are nearly right. You have to consider your free body diagram a bit more carefuly. There are 3 forces involved.

1. The atmospheric pressure acting down on the cover. F = PxA.
2. The chamber pressure acting up on the cover. F = PxA
3. The force of you pulling up on the cover.

Solve the diagram for the force of you pulling.
 

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