# Homework Help: Mechanics -- Object sliding again with friction

1. Oct 16, 2014

### prehisto

1. The problem statement, all variables and given/known data
first of all- yes,i looked in to similar topics,did not succeed :(

My problem : The objects slides down on a plane which located 45degrees with respect to surface. It slides s=0.36m down, it reaches v=2m/s. I have to calculate the coefficient of friction.

2. Relevant equations

3. The attempt at a solution

There is image( sorry for some reason, i could not upload it directly to here)

http://postimg.org/image/uof2i65zv/ [Broken]

So the friction coef. F_friction=(mu)*F_reaction -> (mu)=F_f/F_r
From image above, its easy to see,that tan(alpha)=mu,so it seems too easy.

And what for i need s and v values? I suppose it could be because i just calculated the static friction ,not the dynamic,yes? If i should calculate the dynamic one,could someone help ,please?

Last edited by a moderator: May 7, 2017
2. Oct 16, 2014

### NTW

I think that you should start with a clear sketch of the inclined plane, with the sliding object and the forces involved... I've seen your image, and it doesn't seem clear to me...

3. Oct 16, 2014

### prehisto

I cant imagine what can i ad, there is Force of friction,reaction and mg, corresponding counter forces..

4. Oct 16, 2014

### NTW

The essential vectors that you should draw clearly are:

1) The weight mg
2) One of its components, normal to the plane
3) The other component, parallel to the plane
4) The friction force.

5. Oct 16, 2014

### prehisto

http://postimg.org/image/6ztyvaf4r/ [Broken]

F_F is the friction force.
And now there is components of mg!

Last edited by a moderator: May 7, 2017
6. Oct 16, 2014

### NTW

You should list those forces, one by one, as functions of mg. Then, write down the expression of the net force along the plane.

After that, you should ask yourself: does the object accelerate in his sliding motion? And by how much?

There may be other approaches to the problem, of course. That's just my way of solving it, that I believe correct...