In rotational mechanics i am mostly confused with the axis of rotation. Let me give you some examples of question.

about which axis. Is that instantaneous axis of rotation.
OK this may seem to be solved here but what about this question.

Now once again. which axis should i choose.
IAOR(instantaneous axis of rotation). I can;t find that.
However when i see solution of this example they take torque around the center of the rod and solve it. Why they take center of the rod. Why not any other point. If any other point on the plane is taken then answer may vary.
this point is really confusing me in rotational dynamics. which axis should i choose when i do questions.

please help me.!!!!!

I think general physics is correct place for this question.

In second question, Take axis around point where rod touches the surface.
[tex]I=\frac{ml^2}{3}[/tex]
[tex]T(Torque)=mgl[/tex]

[tex]T=I\alpha[/tex]
[tex]\alpha=\frac{T}{I}[/tex]
[tex]\alpha=\frac{mgl}{\frac{ml^2}{3}}[/tex]
[tex]\alpha=\frac{3g}{l}[/tex]
Now take the center as the axis. Your answer will [tex]\frac{6g}{l}[/tex]. That's different.
How will you explain this with our answer.