# Homework Help: Static friction

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1. Apr 26, 2017

### generalguiness

1. The problem statement, all variables and given/known data
A 50kg object begins at rest on a surface with a static coef of friction at 0.6. If you push horizontally on the object with a force of 27N, how quickly will it move across the surface?

2. Relevant equations

3. The attempt at a solution

This is from Trivium Praxis test prep book. The solution given is 0.6*50=30N of static friction, so no, it will not move. In the very brief section explaining friction, it said that friction=coef * normal force, but they labelled it as capitol N. Shouldnt the normal force be 50g? So F=0.6 * 50g? I decided to try to pass the test this summer after taking physics 15+ years ago!

Last edited by a moderator: Apr 26, 2017
2. Apr 26, 2017

### Staff: Mentor

There's likely a typo in the question. The object description was probably meant to give its weight as 50 Newtons, not mass in kilograms.

3. Apr 26, 2017

### TomHart

Welcome to Physics Forums.
Are you sure it is a 50 kg object, and not a 50 Newton object?
But assuming it is a 50 kg object: If it is a horizontal surface, the normal force N will be equal to the weight of the object. The weight is mg = (50 kg)(9.8 m/s^2) = 490 N (where N is Newtons)
So the normal force will be N = 490 N. And the maximum friction force will be f = μN = (0.6)(490) = 294 N. So if you push with 27 N, the friction force will also be 27 N. Thus the object will not move.

4. Apr 26, 2017

### generalguiness

Thanks. This is the 2nd error I think I've found and I've only done 12 questions in of the first section!