Imagine you have a system of two buckets as shown below. The buckets are spinning about an axle with frictionless bearings at some angular velocity,...

Imagine you have a system of two buckets as shown below. The buckets are spinning about an axle with frictionless bearings at some angular velocity,  .

It starts to rain. What happens to the two-bucket system? Think about angular momentum

a.  must decrease to conserve angular momentum because because the rain increases the mass of the system (which increases the moment of inertia).

b.  remains constant to conserve angular momentum because the amount of rain falling into one bucket equals the amount of rain falling into the other bucket. Any changes due to the rain therefore cancel.

c.  remains constant to conserve angular momentum because the rains kinetic energy is in the downward direction and does not affect the momentum of the buckets, which is in the horizontal plane.

d.  must increase to conserve angular momentum because because the rain increases the mass of the system (which increases the moment of inertia).