# Homework Help: Pulley problem with moment of inetia

1. May 11, 2013

### Iansno1

Problem

As shown below, Block A has mass 'M' and rests on a surface with a coefficient of kinetic friction 'Uk' .The cord attached to A passes over a pulley at C and is attached to a block B of mass '2M'. If B is released calculate the acceleration of A.

Assume the cord does not slip over the pulley. The Pulley can be approximated as a thin disk of radius 'r' and mass 'M/4' . Neglect the mass of the cord

Relevant equations

moment of inertia of the disk: I=0.5*M*r2

Not sure where to start

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2. May 11, 2013

### ehild

with free body diagrams?

ehild

3. May 11, 2013

### Iansno1

How does the Moment of inertia come into the equation? I can do these problems when the pulley is assumed to have no mass and no friction.

4. May 11, 2013

### Staff: Mentor

Moment of inertia is the analog of mass for rotational motion. The moment of inertia resists angular acceleration in the same fashion as mass resists linear acceleration.

In this problem the pulley adds resistance to the acceleration of the overall system because the cord does not slip, and so must cause angular acceleration of the pulley. The angular acceleration is related to the linear acceleration (how?).