# Homework Help: Linear and angular momentum problem

1. Dec 30, 2012

### barryj

This is not a homework problem.
I am trying to set up the following problem. I am doing something wrong. Help. I have attached the problem and figure but here is the text.

Figure 10-52 shows a thin, uniform bar of Length L and mass M and a small blob of putty of mass m. The system is supported by a frictionless horizontal surface. The putty moves to the right with a velocity v, strikes the bar at a distance d from the center of the bar, and sticks to the bar at the point of contact. Obtain expression for the velocity of the system's center of mass and for the angular speed following the collision.

To find the angular speed, I use the conservation of angular momentum.

mv(1)d = m*v(2)*d + (1/12)ML^2 * V(2)

Is this a correct setup?

Thanks
Barry

#### Attached Files:

• ###### physics 10-61.jpg
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2. Dec 30, 2012

### Staff: Mentor

Compute the angular momentum about the center of mass of the system.

3. Dec 30, 2012

### barryj

Thanks Doc Al, I think I see your point. When the putty hits the bar, the rotation is about the center of mass of the rod/putty combination and will be between the center of the rod and the putty as I how on my attachment. Yes?

#### Attached Files:

• ###### center of mass.jpg
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4. Dec 30, 2012

### Staff: Mentor

Yes, that's correct. Now figure out the speed of the bullet and the bar in the center of mass frame.