How Does Angular Velocity Change After Inelastic Collision?

[Jalo]

Homework Statement

A mass m₁ with speed v_1i colides with a mass m₂ of length 1m, initially at rest, and gets stuck with it.
(a) Express the angular velocity in functon of v_1i. (m=m₁=m₂)

Homework Equations

w=v/r

The Attempt at a Solution

Since the collision is totally inelastic I can say
m₁*vi₁=(m₁+m₂)v_f ⇔
Since all masses are equal I can say
v_i1=2v_f⇔v_f=v_1i/2
Since w=v/r
w=v_f/r⇔w=0.5*v_1i/0.5⇔w=v_1i

This is wrong for some reason... Can anyone lead me in the correct way?

Thanks.
D.

 

[JtValentine]

If the length of the bar is 1, then the radius of a circle that the bar makes as it rotates 360 degrees means r=1. Thus w= 0.5V1i/1 = V1i/2.

 

[Doc Al]

I don't quite understand the diagram. What's that ball like thing on top of m2? Is m2 fixed at some point?

 

[JtValentine]

I don't quite understand the diagram. What's that ball like thing on top of m2? Is m2 fixed at some point?

Doc Al has a great point. More explanation is needed. I just assumed the ball at the top of the bar was an axis of rotation, but I could be wrong.

 

[Jalo]

It doesn't say nothing about the ball, so I'm pretty sure it's the axis of rotation

 

[Doc Al]

It doesn't say nothing about the ball, so I'm pretty sure it's the axis of rotation

Assuming that m2 is constrained to rotate about that axis, you cannot apply conservation of linear momentum. (The axis will exert forces on m2.)

But what other quantity is conserved?

 

[Jalo]

Angular momentum?

 

[Doc Al]

Angular momentum?

Right!