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Frictional force problem(box sliding down between two walls)

  • Thread starter Kararr
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  • #1
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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 ):
 

Answers and Replies

  • #2
Doc Al
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Since the velocity is constant, what can you say about the net force on the box?
 
  • #3
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Since the velocity is constant, what can you say about the net force on the box?
oh so is frictional force= 20 N? What about the normal force though? Sorry a bit confused
 
  • #4
Doc Al
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oh so is frictional force= 20 N?
Yes, the total friction force is 20 N.

What about the normal force though?
Who cares? ;)
 
  • #5
CWatters
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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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