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Physics/measurement of force


QUESTION: There are 2 containers A and B of dimensions 1 cm*1 cm*1 cm kept at a height of 5 and 0 cm respectively from the ground. Container B is filled with water and fitted with a water tight piston. The containers are connected  to each other by a pipe. A force was applied on the piston and the water from B got pushed up to A. What is the smallest possible magnitude of the force applied on the piston?

ANSWER: Then apply Pascal's law and equations for work, you'll find the answer.  :)  If you need a hint, you know where to find me.

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QUESTION: I referred to several books but I am not able to find the answer. So yeah, a hint would be nice.

ANSWER: OK, since the mention of Pascal's law didn't work then you just need to realize that the question was badly posed.  No one mentioned the area of the pipe, so no one can possibly calculate the force used without the area dimension of the pipe itself.

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QUESTION: Thank you for pointing that out. What would be the answer if the area of the pipe is 0.09 cm sq.?

Now this sounds like a homework question...but basically the the force multiplied by the area would have to nullify the change in energy density, which would be the pressure change due to the distance (fluid density times g times vertical distance).  Energy density through a fluid is shared equally within the fluid.


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Dr. Stephen O. Nelson


I can answer most basic physics questions, physics questions about science fiction and everyday observations of physics, etc. I'm also usually good for science fair advice (I'm the regional science fair director). I do not answer homework problems. I will occasionally point out where a homework solution went wrong, though. I'm usually good at explaining odd observations that seem counterintuitive, energy science, nuclear physics, nuclear astrophysics, and alternative theories of physics are my specialties.


I was a physics professor at the University of Texas of the Permian Basin, research in nuclear technology and nuclear astrophysics. My travelling science show saw over 20,000 students of all ages. I taught physics, nuclear chemistry, radiation safety, vacuum technology, and answer tons of questions as I tour schools encouraging students to consider careers in science. I moved on to a non-academic job with more research just recently.

Ph. D. from Duke University in physics, research in nuclear astrophysics reactions, gamma-ray astronomy technology, and advanced nuclear reactors.

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