Teaching Physics with the Physics Suite

Edward F. Redish

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Hanging Blocks*

Three cubical blocks of equal volume are suspended from strings. Blocks A and B have the same mass and block C has less mass. Each block is lowered into a fish tank and they hang at rest as shown in the figure at the right.

  1. Is the force exerted by the water on the top surface of cube A greater than, less than or equal to the force exerted by the water on the top surface of cube B? Explain..
  2. Is the force exerted by the water on the top surface of cube A greater than, less than or equal to the force exerted by the water on the top surface of cube C? Explain..
  3. Is the force exerted on the water by block C greater than, less than or equal to the force exerted on the water by block A? Explain.
  4. Rank the buoyant forces acting on the three blocks from largest to smallest. If any buoyant forces are equal indicate that explicitly. Explain.

* from M. E. Loverude, Investigation of student understanding of hydrostatics and thermal physics and the underlying concepts from mechanics, Ph.D. Thesis, University of Washington, 1999.


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Page last modified October 9, 2002: M01