Need help with Friction

1. Mar 14, 2005

SanityMan

Okay, here is the problem I am working on...

A block of a certain weight(w2) is sliding down an inclined plane at angle theta. There is a plank on top of the block with a certain weight (w2) that is attacked to a cord at the top of the plane so that it does not move.

I need to find the coefficient of kinetic friction in terms of the masses of each block and the angle theta. The coeffecient is the same between both surface contacts.

I am using Newton's 2nd law and I'm stuck with the friction. In my free body diagram I am not sure which direction the force of friction is going between the block and the plank nor how it affects both.

2. Mar 15, 2005

cepheid

Staff Emeritus
Since you're trying to figure out directions, hopefully you defined a coordinate system first. After you've done that, think about this: in what direction is the block trying to slide past the plank? Friction always opposes this motion Likewise for the block sliding down the inclined plane.

3. Mar 15, 2005