- #1
discoverer02
- 138
- 1
Here's the problem and I'm close to the answer, but I guess close isn't good enough on a Physics exam.
A spinning solid disk, rotating with angular velocity Wo, is put down on a level surface. It slides and rolls until it reaches an angular velocity W at which it rolls without sliding. Show that W = Wo/3
I place my origin on the ground so that angular momentum is conserved.
The disk spins clockwise
1 = right when the disk is placed on the floor.
2 = right when the disk begins rolling without spinning.
L = angular momentum.
cm = center of mass.
I = moment of inertia about cm
R = radius
M = Mass
V = Velocity of cm
L1spin + L1cm = L2spin + L2cm
IWo + 0 = IW - RMV ==> with no slip V = RW
(2/5)MWoR^2 = (2/5)MWR^2 - MWR^2
-2Wo/3 = W
Besides probably messing up the signs, why do I end up with twice what I need?
A spinning solid disk, rotating with angular velocity Wo, is put down on a level surface. It slides and rolls until it reaches an angular velocity W at which it rolls without sliding. Show that W = Wo/3
I place my origin on the ground so that angular momentum is conserved.
The disk spins clockwise
1 = right when the disk is placed on the floor.
2 = right when the disk begins rolling without spinning.
L = angular momentum.
cm = center of mass.
I = moment of inertia about cm
R = radius
M = Mass
V = Velocity of cm
L1spin + L1cm = L2spin + L2cm
IWo + 0 = IW - RMV ==> with no slip V = RW
(2/5)MWoR^2 = (2/5)MWR^2 - MWR^2
-2Wo/3 = W
Besides probably messing up the signs, why do I end up with twice what I need?