Finding a max angular acceleration

[jhayes25]

Given is a 6' long 40 lb bar hung horizontally by a pin O at its end. It is released from its horizontal position and hits a stopper after reaching a 30 degree angle with the horizontal position at which it started. I am asked to find the value x for which the angular velocity is a maximum and also the corresponding angular acceleration alpha


Sum of the torques about O=I(alpha)
a(t)=r*alpha


I honestly do not know where to start with this one. do I start by summing moments about O?
Thanks in advance for any help.

 

[tiny-tim]

Given is a 6' long 40 lb bar hung horizontally by a pin O at its end. It is released from its horizontal position and hits a stopper after reaching a 30 degree angle with the horizontal position at which it started. I am asked to find the value x for which the angular velocity is a maximum and also the corresponding angular acceleration alpha

Hi jhayes25!

(what's x? )

Hint: use the moment of inertia of the bar about its end, and net torque = rate of change of angular momentum.