Homework Help: Angular acceleration and Torque when rod reaches vertical position?

1. Apr 30, 2012

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 = Iā giving ā = 21.9 rad/s^2...but how do I solve for when it hits vertical position...? Please help!

2. Apr 30, 2012

PhanthomJay

Re: Angular acceleration and Torque when rod reaches vertical position??

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

3. Apr 30, 2012

sweetpete28

Re: Angular acceleration and Torque when rod reaches vertical position??

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

4. Apr 30, 2012

PhanthomJay

Re: Angular acceleration and Torque when rod reaches vertical position??

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

5. Apr 30, 2012

sweetpete28

Re: Angular acceleration and Torque when rod reaches vertical position??

Both would be 0 then, right?

6. Apr 30, 2012

PhanthomJay

Re: Angular acceleration and Torque when rod reaches vertical position??

Right!