# Box on a board, acceleration

1. Dec 21, 2013

### hvthvt

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

A small box of mass m1 is sitting on a board of mass m2 and length L. The board rests on a frictionless horizontal surface. The coefficient of static friction between the board and the box is, as usual, less than Î¼s. The board is pulled with a force F, as shown. We wish to know the minimum force necessary to pull the board out from under the box. Express your answers in terms of any of the variables F, L, Î¼s,g, m1 and m2.

Find the acceleration of the board when the force of static friction reaches its maximum possible value.

What is the requirement for the board starting to slide under the box?

2. Relevant equations

F=ma

3. The attempt at a solution

I already solved the largest possible acceleration of the box, which is
F=(m1+m2)a up untill m1 falls. I do not actually understand how I can find the maximum possible value. This is probably when the acceleration is the largest I guess?.. Can anybody help me out with these two questions please! Thank you in advance

2. Dec 21, 2013

### Pythagorean

3. Dec 22, 2013

### haruspex

No, that coefficient is usually written Î¼s. It would not be less than Î¼s. Do you mean the coefficient of kinetic friction?
What did you get for that?
That is not right. F is unlimited, so it would make a unlimited.
Draw a FBD diagram for the box. What are the forces on it?