- #1

FredericChopin

- 101

- 0

## Homework Statement

http://imgur.com/C0XYEKw

## Homework Equations

F

_{net}= m*a

F

_{G}= m*g

f

_{static}= μ*N

## The Attempt at a Solution

If both Block 1 and Block 2 have acceleration a in the x-direction and have an acceleration of 0 in the y-direction, then the force of static friction on Block 1 due to Block 2 doesn't seem to depend at all on what Block 2 is doing. This is because the normal force on Block 1 due to Block 2 is still the same as it is at rest and the force of static friction on Block 1 due to Block 2 is the only force acting in the x-direction on Block 1.

I tried this by considering only Block 1 as a system.

In the y-direction, the forces acting on Block 1 are the normal force on Block 1 due to Block 2, N

_{12}, and the gravitational force on Block 1 due to the Earth, F

_{1E}. The acceleration, a

_{y}, is equal to 0.

Thus:

Σ F

_{net,y}= 0 = N

_{12}- F

_{1E}= N

_{12}- m

_{1}*g

Thus:

N

_{12}= m

_{1}*g

In the x-direction, the only force acting on Block 1 is the force of static friction, which is acting in the right, positive x-direction. The acceleration, a

_{x}, is equal to a.

Thus:

Σ F

_{net, x}= m

_{1}*a = f

_{static}= μ*N

_{12}= μ*m

_{1}*g

Thus the force and direction of the force of static friction on Block 1 due to Block 2 is:

f

_{static}= μ*m

_{1}*g

This, however, is the wrong answer.

I don't understand why though. Where am I going wrong?

Thank you.