# 2 masses, 3 pulleys

1. Dec 16, 2015

### Gbox

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

Find the acceleration of the masses

2. Relevant equations
$F=Ma$

3. The attempt at a solution
We know that the system is moving so for $M_1$ we have $M_1gsin\theta$ on the other hand on $M_2$ we have $M_1gsin\theta-M_2gsin\theta$

How can I conclude that the acceleration of $M_2$ is twice of $M_1$?

2. Dec 16, 2015

### haruspex

I assume you meant the other way around.
It follows from the assumption that the string length does not change.

3. Dec 16, 2015

### Gbox

Sorry $M_1$ is twice the acceleration as $M_2$.

Yes the string length does not change

4. Dec 16, 2015

### haruspex

Do you see how it follows from that?

5. Dec 16, 2015

### Gbox

No I can't understand the forces map

6. Dec 16, 2015

### haruspex

It's not to do with the forces. Consider the lengths of the three sections of strings. They add up to a constant, and two are always the same as each other. That allows you to express two in terms of the third. Then see how they relate to the two accelerations.