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## Homework Statement

[/B]

An Atwood's machine consists of two masses, m

_{A}and m

_{B}, which are connected by an inelastic cord of negligible mass that passes over a pulley. If the pulley has radius R

_{0}and moment of inertia I about its axle, determine the acceleration of the masses m

_{A}and m

_{B}.

## Homework Equations

[/B]

L = mvr

T = dL/ dt

## The Attempt at a Solution

[/B]

This is an example from my textbook. The solution involves:

angular momentum about the axle = (m

_{A}+m

_{B})vR

_{0}+ Iv/

_{R0}

torque about the axle =

**m**

_{B}gR_{0}- m_{A}gR_{0}Then it uses the equation T = dL/dt and finds accelerations of the masses.

What confuses me is the way it calculates the torque. When we were solving this exact same problem in rotational motion, the equations were like these:

m

_{B}*g - F

_{TB}= m

_{B}*a

F

_{TA}- m

_{A}*g = m

_{A}*a

**(F**

_{TB}- F_{TA})*r = I*a/rHow can angular momentum solution get rid of tensions in the torque equation?

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