Question

Falling beam.
The picture shows a simple beam fastened to a wall.
The beams length is L, its mass is M and $\theta$ is the angle.
The bottom end of the beam turns around a frictionless axis but the upper end of the beam is held up with a string.
Now the string breaks.
Write the angular acceleration at that moment as a function of g, L, and $\theta$ .

How do I begin to solve this problem?

Answer 1

about that axis

torque = force *distance

=mg *L/2 *cos(theta)

by newton's law

torque = I *acceleration

I = mL^2/3

acceleration =(mgL/2cos(theta)) /mL^2/3

=3/2 *g*cos(theta) *1/L