Teaching Physics with the Physics Suite

Edward F. Redish

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Tricking Bill

A student, whom we will call Bill, was about to go out on a date when his roommate, Bob, asked him to hold a pail against the ceiling with a broom for a moment. After he had complied, the roommate mentioned that the pail was filled with water and left.

  1. Draw a free-body diagram showing all the forces acting on the pail. Be sure for each force you identify the kind of force and the object whose interaction with the pail is responsible for the force.
  2. Suppose Bill wants to slide the pail a few feet to one side so he can get to a chair in the room. Are any other forces not specified in your answer to part (a) that become relevant?
  3. Suppose the pail weighs 1 pound, it has 6 pounds of water in it, the coefficient of friction between the broom and pail is 0.3, and the coefficient of friction between the pail and the ceiling is 0.5. Can Bill slide the pail? Explain

Note to the instructor: This is a bit subtle and definitely challenging. Not for an exam!

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Page last modified October 15, 2002: D24