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## Homework Statement

http://img148.imageshack.us/img148/8686/ssslk.png [Broken]

the two boxes and the pulley have the same mass

I=.5mr^2

the system is accelerating downwards calculate the magnitude of the acceleration

## Homework Equations

## The Attempt at a Solution

I will call the falling one D and the higher one U

mg-T

_{d}=ma

T

_{d}=mg-ma

T

_{u}=ma

by torque

T

_{d}-T

_{u}=I alpha/r

T

_{d}-T

_{u}=I a/r^2

T

_{d}-T

_{u}=(.5mr^2) a/r^2

T

_{d}-T

_{u}==.5ma

mg-ma-ma=.5ma

2.5a=g

a=g/2.5=3.5

what's wrong here??

in the exam I got 4 out of 5 in this question I can't see why I didnt get a full mark I revised everything

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