*Answer:* The moment of inertia of a rod of mass and length about
an axis, perpendicular to its length, which passes through one of its ends is
(see question 8.3). Hence,

The angular equation of motion of the rod is

where is the rod's angular acceleration, and is the net torque exerted on the rod. Now, the only force acting on the rod (whose line of action does not pass through the pivot) is the rod's weight, . This force acts at the centre of mass of the rod, which is situated at the rod's midpoint. The perpendicular distance between the line of action of the weight and the pivot point is simply

Thus, the torque acting on the rod is

It follows that the rod's angular acceleration is written