# Kinetic friction question

1. Sep 11, 2006

### tismisskris

This homework set has stumped me for the past 2 days. It's due at midnight, and I still don't understand.

One of the questions asks for an algebraic formula to find the magnitude P P of the forces with which two blocks sliding on a horizontal surface together push against each other? Express your answer in terms of the mass m1 of block 1, the mass m2 of block 2, and the magnitude fk of the kinetic frictional force that acts on block 2. The direction to the right in the drawing is the positive direction.

The closest I've got was

P= (m1a1 - m2a2 - fk) The problem is they don't ask for acceleration.

I am confused on how to find the magnitude that block 1 is pushing on block 2 without knowing the acceleration.

I tried to use the formual Fnet= Fapplied - Fkinetic friction, but it doesn't work.

Any help is greatly appreciated.

Kristen

2. Sep 11, 2006

### Staff: Mentor

I'm guessing that the blocks are not accelerating, just moving with a constant velocity (not sure about that without seeing the whole problem). So the force that goes into pushing them along does not go into changing their velocity -- just into overcoming the counter-force of friction. What can you say about the frictional forces involved, in terms of the blocks' masses and their coefficients of friction?