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Homework Help: Frictional force problem(box sliding down between two walls)

  1. Sep 20, 2014 #1
    The full problem is: "A 2.0kg box slides down at constant velocity between two identical walls. What is the frictional force exerted on the box by one of the walls?"

    The answer I got was zero because I equated Normal force (of the wall on the box) at zero.
    Am I wrong? ): Does the weight of the box press against the wall as well?

    Please help ):
  2. jcsd
  3. Sep 20, 2014 #2

    Doc Al

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    Staff: Mentor

    Since the velocity is constant, what can you say about the net force on the box?
  4. Sep 20, 2014 #3
    oh so is frictional force= 20 N? What about the normal force though? Sorry a bit confused
  5. Sep 20, 2014 #4

    Doc Al

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    Staff: Mentor

    Yes, the total friction force is 20 N.

    Who cares? ;)
  6. Sep 20, 2014 #5


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    Science Advisor
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    Gold Member

    I can see the confusion about the normal force...

    In most friction problems gravity provides a normal force. However in this problem something (unspecified) is causing the walls to press on the sides of the box creating a normal force and hence friction with them. Perhaps the box is made of rubber and is just a tight fit between the walls? Whatever the cause you don't need to care about it.

    The problem isn't a problem about friction at all. It's about Newtons laws.
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