A solid disk is rotating about an axis with uniform angular velocity. Another disk (with the same moment of inertia about the rotation axis) is dropped on top of it. After the collision, both disks are rotating together at a new uniform angular velocity. How is the new angular velocity related to the old one

The period of a pendulum varies directly as the square root of the length of the pendulum and inversely as the square root of the acceleration due to gravity. find the period when the length is 144 cm and the acceleration due to gravity is 980 cm per second squared, if the period is 7pi seconds when the length is 289 cm and the acceleration due to gravity is 980 cm per second squared.