# What is the angular momentum of a rod with a mass of #2 kg# and length of #9 m# that is spinning around its center at #12 Hz#?

##### 1 Answer

The angular momentum is given by

where

For a thin rod with uniform density rotating about the centre, the moment of inertia is given by

You can find moment of inertia formulas for different shaped objects tabulated. In this case

We want to work in SI units, so convert the frequency to angular velocity using

This arises because each rotation is

Finally, substitute these values into the equation to calculate the angular momentum

Notice that we ditch the radians in the units. This is a a thing that I don't really understand but is due to the definition of the radian being a ratio of two lengths (so units cancel out). It gets used and dropped sporadically.

#equalrightsforallunits

Careful with significant figures too.