# Homework Help: How much force does the 4kg block exert on the 6kg block?

1. Sep 27, 2007

### aligass2004

1. The problem statement, all variables and given/known data
Blocks with masses of 1kg, 4kg, and 6kg are lined up in a row on a frictionless table. All three are pushed forward by a 13N force applied to the 1kg block. a.) How much force does the 4kg block exert on the 6kg block? b.) How much force does the 4kg block exert on the 1kg block?

2. Relevant equations

F=ma
F=uk(n)
3. The attempt at a solution

I'm not sure what's all included in the free body diagrams. I know gravitational force is pushing down on all three blocks, and I know a normal force is pushing up on all three blocks. I also know that a force is pushing on the 1kg block.

2. Sep 28, 2007

### learningphysics

First take the 3 blocks as one system... write the $$\Sigma{F} = ma$$ equation for this system... that will allow you to solve for acceleration.

For part a), examine the freebody diagram of the 6kg block... write the $$\Sigma{F} = ma$$ equation... you can solve for the force you need... you already have acceleration from the first part.

For part b), examine the freebody diagram of the 1kg block... do the same type of thing as with part a).

3. Sep 29, 2007

### aligass2004

For the acceleration, I got 1.182 m/s^2. For part A, I got the force to be 7.092. I'm still having trouble with part B though. The equation would be -F = m(ax), which would give -1.182.

4. Sep 29, 2007

### learningphysics

What are the forces acting on the 1kg block? The vector sum of these forces = max

5. Sep 29, 2007

### aligass2004

I got it. I completely forgot to add the force given to the whole system.