Why is friction acting in the tangential direction?

[eurekameh]

http://imageshack.us/photo/my-images/440/49789320.png/
Assuming the indicated direction of motion, why is friction acting as shown in the tangential direction? Shouldn't it be acting in the opposite direction?

 

[SammyS]

http://imageshack.us/photo/my-images/440/49789320.png/
Assuming the indicated direction of motion, why is friction acting as shown in the tangential direction? Shouldn't it be acting in the opposite direction?

Is there some information you're not letting us in on? For instance, is the turntable undergoing negative angular acceleration?

 

[eurekameh]

The turntable is actually undergoing positive angular acceleration with its motion shown counter-clockwise.
We're looking for the time it takes for the turntable to reach a speed great enough to break the cord, which can only sustain a maximum tension of 100 N. mu,s = 0.1 and the mass of the disk D is 3 kg.

 

[SammyS]

Then friction must have a tangential component as well as a radial component as shown in the figure.

 

[eurekameh]

Friction only has a tangential component as shown in the figure. The T in the radial component is the tension in the string. My question is: why is the friction force acting in the positive tangential direction, if friction opposes motion?

 

[eurekameh]

Bump.