Linear and angular momentum problem

Click For Summary

Homework Help Overview

The discussion revolves around a problem involving linear and angular momentum, specifically focusing on a collision between a moving blob of putty and a uniform bar. The scenario is set on a frictionless horizontal surface, and participants are exploring the implications of conservation laws in this context.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • The original poster attempts to establish the conservation of angular momentum to derive expressions for the system's center of mass velocity and angular speed post-collision. Some participants question the setup of the angular momentum equation and the point about which it is calculated.

Discussion Status

Participants are actively engaging with the problem, with some providing guidance on the correct approach to consider the center of mass of the combined system. There is acknowledgment of the need to clarify the point of rotation during the collision.

Contextual Notes

The original poster indicates uncertainty in their setup and seeks validation of their approach, suggesting that there may be constraints or specific assumptions in the problem that need to be addressed.

barryj
Messages
856
Reaction score
51
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
 

Attachments

  • physics 10-61.jpg
    physics 10-61.jpg
    26.3 KB · Views: 659
Physics news on Phys.org
Compute the angular momentum about the center of mass of the system.
 
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?
 

Attachments

  • center of mass.jpg
    center of mass.jpg
    14.7 KB · Views: 862
barryj said:
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?
Yes, that's correct. Now figure out the speed of the bullet and the bar in the center of mass frame.
 

Similar threads

Replies
5
Views
2K
Replies
335
Views
17K
  • · Replies 17 ·
Replies
17
Views
1K
  • · Replies 10 ·
Replies
10
Views
2K
Replies
17
Views
2K
Replies
3
Views
2K
  • · Replies 12 ·
Replies
12
Views
2K
Replies
10
Views
3K
  • · Replies 18 ·
Replies
18
Views
4K
Replies
5
Views
3K