# Frictional force problem(box sliding down between two walls)

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?

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Doc Al
Mentor
Since the velocity is constant, what can you say about the net force on the box?

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

Doc Al
Mentor
oh so is frictional force= 20 N?
Yes, the total friction force is 20 N.

What about the normal force though?
Who cares? ;)

CWatters
Homework Helper
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.

• Kararr