# Solving a Physics Problem Using Archimedes Principle

• Tanya Sharma
In summary, the conversation discusses a problem involving a hemisphere submerged in fluid and the force exerted by the fluid on the hemisphere. The group discusses different methods of solving the problem, including using Archimedes' principle and Pascal's law. They also discuss the difference between the force due to pressure on the curved surface versus the flat surface of the hemisphere. Ultimately, they conclude that Archimedes' principle may not be directly applicable to this problem, but it can be used as a starting point for finding the correct answer.
Should I think of the portion of ball on the left in isolation ? I mean should I consider the forces acting on the ball(truncated sphere) on the left side?

If yes , then

Force due to fluid on left+Force due to wall +Force exerted by the portion of ball towards right on the left portion = 0 .

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Let's say you want the force that the fluid on the left side of the wall exerts on the ball in your picture in #34. This is the same as the force that the fluid in my picture exerts on the curved portion of the truncated sphere if Po = 3p. But in my picture you can relate this force to the force that the fluid exerts on the flat portion of the truncated sphere.

When I first came across this problem , I got the answer right . But on second thoughts my reasoning seemed too muddled up.

I have understood your post#35 . In your picture the force due to fluid on left would be equal and opposite to that of force exerted on the flat surface = ##3pπR^2## .

But I am sorry I am not able to relate your picture with the setup I posted in post#34 .

TSny said:
But in my picture you can relate this force to the force that the fluid exerts on the flat portion of the truncated sphere.

Which fluid is exerting force on the flat surface of truncated sphere (on the left), the one with pressure P or 3P ? There is also the wall exerting force on the flat surface . In addition, there would be force from the remaining part of the sphere (the one on the right) .

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In post #35, the purpose was to see that the fluid exerts a force on the curved surface of ##3p\pi R^2## by comparing with the force on the flat portion. Now you can forget the flat portion and conclude that whenever the curved portion is exposed to a fluid of uniform pressure ##3p##, the force on the curved portion will be ##3p\pi R^2##. In your problem, the curved portion of the sphere on the left of the wall is exposed to a pressure of ##3p##. So, the force on that portion will be ##3p\pi R^2##. I think that's a valid argument unless I am overlooking something.

Tanya Sharma
Thank you very much

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