# Homework Help: The magnitude of the force of friction

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1. Dec 22, 2015

### Anon1456

solved

Last edited: Dec 22, 2015
2. Dec 22, 2015

### Isaac0427

I am not an expert but I believe that equation only applies to gravity. It would be mu (the friction coefficient) times the force applied to the box (which, because your mass is 1 in this case, is equal to the acceleration before friction). The g you used in your post, that is equal to 9.81 m/s^2 is calculated from newton's equation F=GM/r^2. That is not the force being applied to the box. I hope that helps!

3. Dec 22, 2015

### Isaac0427

By box I meant the object. I ususually think of these objects as boxes.

4. Dec 22, 2015

### Mister T

Net force equals mass times acceleration.

5. Dec 22, 2015

### jbriggs444

There are two general strategies that can be used to solve this exercise.

One uses the starting point that Mister T suggests -- Express acceleration in terms of the applied force. If you can solve the equations of motion for the acceleration, you can extract the force from that.

The other uses the notion of work and kinetic energy. You are told the distance covered and you can compute the energy that must be lost...