# What torque would have to be applied to a rod with a length of #7 m# and a mass of #9 kg# to change its horizontal spin by a frequency #12 Hz# over #9 s#?

##### 1 Answer

Jan 24, 2018

The torque for the rod rotating about the center is

The torque for the rod rotating about one end is

#### Explanation:

The torque is the rate of change of angular momentum

The mass of the rod is

The length of the rod is

The moment of inertia of a rod, rotating about the center is

The rate of change of angular velocity is

So the torque is

The moment of inertia of a rod, rotating about one end is

So,

The torque is