# Homework Help: Pulley and mass acceleration

1. Nov 6, 2006

### dtesselstrom

Blocks of mass m1 and m2 are connected by a massless string that passes over the pulley in the figure. The pulley turns on frictionless bearings, and mass m1 slides on a horizontal, frictionless surface. Mass m2 is released while the blocks are at rest.
Suppose the pulley has mass mp and radius R. Find the acceleration of m1.
Find the tension in the upper portion of the string.
Find the tension in the lower portions of the string.
Ive tried R*g*m2/(1/2*mp*r^2)*R and it said it needs mass1 in the problem but I couldnt figure out where it is needed

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2. Nov 6, 2006

### OlderDan

Draw three free body diagrams. One for mass on table. One for hanging mass. One for wheel. You need the moment of inertia of the wheel (looks like you have it) and the torque on the wheel,which comes from the two tensions in the string (not the weights of the masses). The acceleration of both masses and the tangential acceleration of the rim of the wheel have the same magnitude. Relate the angular acceleration of the wheel to the tangential acceleration of its rim.

3. Nov 6, 2006

### dtesselstrom

Ive already drawn out the free body diagrams and in class our teacher told us that this problem is solved with a=-m2*g/(1/2mp+m1+m2) but it told me that was wrong too
so the equations I have are T2-m2*g=m2*a for m2 T1=m2\1*a for m1 and 1/2mpR^2*angular acc.=RT1-RT2

Last edited: Nov 6, 2006
4. Nov 6, 2006

### dtesselstrom

I calculated a new answer
a=2m2*g/(m1+m2) can anyone verify if that is correct because I only have one more guess to get the answer right.

5. Nov 7, 2006

### OlderDan

There has to be an mp in the answer for the acceleration. This cannot be right.

6. Nov 5, 2007

### Mwhit

the correct answer is m2g/(m1+m2+.5mp)

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