A Uniform 2

Multiple Choice

A uniform 2.00-kg circular disk of radius 20.0 cm is rotating clockwise about an axis through its center with an angular speed 30.0 revolutions per second. A second uniform 1.50-kg circular disk of radius 15.0 cm that is not rotating is dropped onto the first disk so that the axis of rotation of the first disk passes through the center of the second disk. What is the final angular speed of the two disks when they are rotating together?

A) 16.9 revolutions per second
B) 19.2 revolutions per second
C) 21.1 revolutions per second
D) 17.1 revolutions per second
E) 12.7 revolutions per second