Calculate Torque: Solve the Equation!

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Homework Statement


http://i.imgur.com/WrwsT.png
Diagram of a spool on a frictionless horizontal surface, shown in top view, with a thread wound around its inner radius r = 0.5 m and outer radius R = 1 m, pulled to the right with tension T. Printed multiple-choice question text sits beside it.


Homework Equations



Torque = FR


The Attempt at a Solution



1) I thought I need two torques because they are in oppsite direction

2) I tried use alpha find acceleration and find angular velocity and K=1/2 I omega^2
 
TBBTs said:

Homework Equations



Torque = FR
What is R in that equation? (Please don't just say "the distance" ... what distance does the R signify?)

The Attempt at a Solution



1) I thought I need two torques because they are in oppsite direction
No, there is only one torque acting on the spool here. There is no friction, and the normal force does not exert a torque.

2) I tried use alpha find acceleration and find angular velocity and K=1/2 I omega^2
You don't need the angular velocity. What is the angular counterpart to Newton's 2nd Law, F=ma?