For every mass, the acceleration is
The acceleration is downward, as indicated by the negative sign.
To solve this problem
Two masses,
and
are connected by a rope across a frictionless pulley in an Atwood machine. The net force on each mass is the difference between the mass's weight and the tension in the rope, which is the same on both sides of the rope.
The net force on mass
is:

The net force on mass
is:

Since the system is in motion, the net force on each mass must be equal to the mass times its acceleration. so, we can set the two equations equal to each other:


Solving for T in the second equation, we get:

Substituting this expression for T into the first equation, we get:

Now, let combining like terms, we get:

Solving for a, we get:

Plugging in the values of m1 and m2, we get:


So, For every mass, the acceleration is
The acceleration is downward, as indicated by the negative sign.