# Homework Help: How does one do this question?

1. Nov 20, 2012

### EPFLstudent

Figure attached below. You have a big block of mass M and a small block of mass m. When m=3kg, the acceleration of the large block is 0.6ms-2. When m=4kg, the acceleration of the large block is 1.6ms-2. The dynamic friction coefficient between the large block and the surface it slides on is μ. There is no friction between any other surface. Questions:

a) Express the relationship between the movement of block m and block M
b) Derive expressions for the motion of block m and block M.
c) Determine the mass of block M and the dynamic friction coefficient, μ, between it and the surface it slides on.

Last edited: Nov 20, 2012
2. Nov 20, 2012

### jbriggs444

Nice problem. So what have you got so far? How does the motion of mass m relate to the motion of mass M?

3. Nov 20, 2012

### EPFLstudent

I know that $x_m = 2 x_M$, so that the small block moves two times as much as the big block. My problem is decomposing the forces.

4. Nov 20, 2012

### SteamKing

Staff Emeritus
Draw free body diagrams. Start with the mass m. What forces are acting on m?