Question

Sample Question Example – Disk dropped on Disk top initial - 0. 1) If both disks have the same moment of inertia (1), what is the angular momentum of the top disk before the collision? What is the angular momentum of the bottom disk before the collision? O top, final = 0 bottom, final = 0, 2) What is the angular momentum of the top disk after the collision? Bottom disk? bottom initial = 0 3) What type of collision is modeled here? 4) Is the angular momentum of the top disk conserved? Bottom disk? Both disks as a system? "is friction between objetos within a system an external force?" 5) Analyzing only the top disk, what force changes its angular momentum? Does this force cause a torque? No !! 6) Analyzing only the bottom disk, what force changes its angular momentum? Does this force cause a torque? smartPhysics Mechanics Lecture 19, Slide 7 7) Analyzing both disks together as a system, is the energy of the disks different after the collision than before the collision? Perfecther than elastic 8) Describe all energy transformations from the initial conditions to the final conditions. Activate Window

Answer 1

Solution:

Moment of inertia of both disks

Initial angular velocity of top disk $\omega _{0}$

Initial angular velocity of bottom disk is zero.

1) Angular momentum of top disk before collision is

$J_{top}=I\omega _{0}$

Angular momentum of bottom disk before collisiom is

$J_{bottom}=0$

2) Angular momentum of the top and bottom disk are equal after collision.

  $J=2I\omega _{f}$

3) Perfectly elastic collision is modelled here.There is conservation of momemtum and energy .

4) Since there is no friction between disks. Yes angular momentum of the top and bottom disk are conserved. And also as a system, its angular momentum is conserved.