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conana
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Homework Statement
A spool of mass m and moment of inertia I (presumably with respect to the CM) is free to roll without slipping on a table. It has an inner radius r, and an outer radius R. If you pull on the string (which is wrapped around the inner radius) with tension T at an angle [tex]\Theta[/tex] with respect to the horizontal, what is the acceleration of the spool? Which way does it move?
The Attempt at a Solution
I got an answer for the first part, but I feel a little unsure about it. Am I on the right track?
[tex]\tau_{CM}=f-rT\cos{\Theta}=I\alpha,\hspace{.1 in}(1)[/tex]
[tex]m\ddot{x}=T\cos{\Theta}-f.\hspace{.1 in}(2)[/tex]
where f is the friction force between the spool and the ground.
The "non-slip" condition gives
[tex]\ddot{x}=R\alpha.\hspace{.1 in}(3)[/tex]
A little algebra on (2) yields
[tex]f=T\cos{\Theta}-m\ddot{x}.\hspace{.1 in}(4)[/tex]
Substituting (3), (4) into (1) gives
[tex]\tau_{CM}=T\cos{\Theta}-m\ddot{x}-rT\cos{\Theta}=I\dfrac{\ddot{x}}{R}[/tex]
[tex]\Rightarrow T\cos{\Theta}(1-r)=\ddot{x}\left(\dfrac{I}{R}+m\right)[/tex]
[tex]\Rightarrow \ddot{x}=T\cos{\Theta}\dfrac{1-r}{m+\dfrac{I}{R}}.[/tex]
[Edit] In the diagram in my book, the string is wrapped counter-clockwise around the inside of the spool so it comes out from the underside on the right and is pulled towards the right ([tex]+\hat{x}[/tex]).
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