Atwood machine question: an Atwood machine with a massless pulley and no friction has equal tension in both sides of the cord connecting the two masses. I'm looking now at a problem which starts with pulley with mass and asks to find the acceleration. Then it says to ignore the pulley's moment of inertia and calculate the acceleration. Here's the problem: it says, as a hint, the tensions in each side of the rope aren't equal. That makes no sense. No parameters with which you could calculate friction exist. How can that be?

Question

Atwood machine question:  an Atwood machine with a massless pulley and no friction has equal tension in both sides of the cord connecting the two masses.  I'm looking now at a problem which starts with pulley with mass and asks to find the acceleration.  Then it says to ignore the pulley's moment of inertia and calculate the acceleration.  Here's the problem:  it says, as a hint, the tensions in each side of the rope aren't equal.  That makes no sense.  No parameters with which you could calculate friction exist.  How can that be?

vincent-lyon.fr · Answer

If the question is worded as you relate it, I agree that the question makes no sense.
In order for the tension to be different on either side, you must have one of the following:
- pulley with non-zero moment of inertia
- pulley with friction torque on its axis.