Disk A, with a mass of 2.0 kg and a radius of 80 cm , rotates clockwise about a
ID: 1529574 • Letter: D
Question
Disk A, with a mass of 2.0 kg and a radius of 80 cm , rotates clockwise about a frictionless vertical axle at 30 rev/s . Disk B, also 2.0 kg but with a radius of 30 cm , rotates counterclockwise about that same axle, but at a greater height than disk A, at 30 rev/s . Disk B slides down the axle until it lands on top of disk A, after which they rotate together. After the collision, what is magnitude of their common angular velocity (in rev/s)? Express your answer using two significant figures. In which direction do disks rotate after the collision? In which direction do disks rotate after the collision? clockwise counterclockwise
Explanation / Answer
According to the given problem,
Using conservation of Angular momentum,
0.8²*30 + 0.3²*(-30) = (0.8² + 0.3²)
= 30(0.8² - 0.3²)/(0.8² + 0.3²)
= 22.6 rev/s
It is clockwise, the same as disk A, as disk A had the largest angular momentum