# Homework Help: Pulley, Motor and Weight Torque Problem

1. Oct 21, 2012

Pulley and Motor - Torque Problem

1. The problem statement, all variables and given/known data
When the motor in the figure below lowers the m = 1140kg mass, it produces a tension of 1.04E+4N in the cable on the right side of the pulley. The pulley has a moment of inertia of 79.7kgm^2 and a radius of 0.741m. The cable rides over the pulley without slipping. Determine the acceleration of the m = 1140kg mass. Use g=9.81m/s^2.
Draw free-body diagrams of the mass and the pulley. Do not assume that the tension in the cable is the same on both sides of the pulley.

2. Relevant equations
T=rxf

a=α*r where α = angular acceleration
----> a/r=α

3. The attempt at a solution
mg-$T_1{}$ = ma
$T_2{}$ = 10 400 N

r*($T_1{}$-$T_2{}$)=I*α
r*($T_1{}$-$T_2{}$)=I*(a/r)
$T_1{}$-$T_2{}$=I*(a/r^2)
(11 183 - 11 40a) - (10 400) = (79.7/0.741^2)a
783-1140a = 145.15a
783 = 1285.15a
a= 0.609 m/s/s

I'm not sure what I'm doing wrong. The steps all make sense to me, but when I've tried submitting the answer on LON-CAPA it says it's incorrect. Anyone have any ideas?

Last edited: Oct 21, 2012
2. Oct 21, 2012

### Spinnor

Can you add a picture, sketch, or scan of the set-up. One picture is worth a lot of words.