Angular acceleration and Torque when rod reaches vertical position?

[sweetpete28]

Angular acceleration and Torque when rod reaches vertical position??

A rod (mass 1.30 kg, length .670 m) attached to a frictionless axis is released from rest in the horizontal position. What is the magnitude of the torque and angular acceleration when the rod has reached the vertical position?

I know at horizontal position (immediately after release) Torque = FR = mg(L/2)= 4.27n-m and torque = I∂ giving ∂ = 21.9 rad/s^2...but how do I solve for when it hits vertical position...? Please help!

 

[PhanthomJay]

When the rod is hanging vertically, what is the moment arm of the weight force about the pivot?

 

[sweetpete28]

Is it 0 b/c it is through the axis of rotation?

 

[PhanthomJay]

Yes, correct. So what's the torque and angular acceleration at this position?

 

[sweetpete28]

Both would be 0 then, right?

 

[PhanthomJay]

Both would be 0 then, right?

Right!