Conservation of Angular momentum question.

[greg_jones20]

Homework Statement

An object of mass 25gm and horizontal velocity of 125 cm/s strikes and sticks to the top of a cylinder of mass 333gm and radius 25cm at rest.
a) Use conservation of angular momentum to determine the final angular velocity of the combination after the collision.
b) What is the change in the kinetic energy of the system?

Homework Equations

Angular Momentum(L) = IW, where I is moment of inertia and W is angular velocity. and
Momentum(P) = mass(m)*velocity(v),

The Attempt at a Solution

Lo = Lf
m1*Vo + I*Wo = If*Wf [here, Wo=0, m1=25gm, If=1/2(m1+m2)R^2, Wf = Vf/R]
(.025kg)(1.25m/s) + 0 = [1/2(.025kg+.333kg)(.25m)^2]Vf
Tried to solve for Vf from above eqn. but couldn't get the units to work out correctly.

 

[vela]

Linear momentum p and angular momentum L are not the same thing. You need to use the angular momentum of the first object, not its linear momentum, in your conservation of angular momentum equation.