 #1
hidemi
 208
 36
 Homework Statement:

A particle of mass m = 0.10 kg and speed v0 = 5.0 m/s collides and sticks to the end of a uniform solid cylinder of mass M = 1.0 kg and radius R = 20 cm. If the cylinder is initially at rest and is pivoted about a frictionless axle through its center, what is the final angular velocity (in rad/s) of the system after the collision?
(A) 8.1
(B) 2.0
(C) 6.1
(D) 4.2
(E) 10
 Relevant Equations:
 Li = Lf = Iω
I calculated as attached and got it right. However, I just wonder why we can't use conservation of energy as the question has already specified 'frictionless', meaning no energy loss and energy distributed to the rotation only.