What torque would have to be applied to a rod with a length of #4 m# and a mass of #3 kg# to change its horizontal spin by a frequency of #2 Hz# over #1 s#?
We asume that the rod is spinning around its centerm this is important for the moment of inertia.
The torque is the rate of change of angular momentum
The moment of inertia of a rod is
The rate of change of angular velocity is
So the torque is