Four discs are spinning at constant angular velocity. Four ideantical balls are dropped on the discs at different distances from the center. The balls are dropped from rest and stick to the disc. Rank the discs in terms of final angular velocity from lowest to highest.

They will have equal final angular velocity.

Explanation:

Since the discs starts from rest and rotates about a fixed axis, they are subject to a constant net torque. The work done by the torque during the second revolution is as the work done during the first revolution.

The four disc will turn through equal angles in equal times.

current and voltage can both be different in different parts of a circuit so it matters where you place the ammeter and voltmete