Block Friction Problem

1. Jun 15, 2009

Patta1667

1. The problem statement, all variables and given/known data

A block of mass $$M_1$$ rests on a block of mass $$M_2$$ which lies on a frictionless table. The coefficient of friction between the blocks is $$\mu$$. What is the maximum horizontal force which can be applied to the lower ($$M_2$$) block for the blocks to accelerate without slipping on one another?

2. Relevant equations

3. The attempt at a solution
The acceleration of the two blocks (assuming they're not slipping) is $$a = \frac{F}{M_1 + M_2}$$, and you want the upper block ($$M_1$$) to not slip, that is, the acceleration times $$M_1$$ must be less than or equal to the frictional force. When the blocks start slipping, $$M_1 a = \mu M_1 g$$ where the frictional force holding the upper block is $$f = \mu M_1 g$$. This means that $$a = \frac{F_{max}}{M_1 + M_2} = \mu g$$, or $$F_{max} = \mu g (M_1 + M_2)$$.

I'm not sure if this answer is right, but it makes intuitive sense when looking at the final equation. Thanks for any help!

 Sorry, posted in wrong section. I can't find a delete button, but any help would still be appreciated

2. Jun 19, 2009

dx

Looks correct.