Rod on a Plane: Calculating Angular and Linear Motion After Impact"

  • Thread starter Thread starter Nexus99
  • Start date Start date
  • Tags Tags
    Plane Rod
Click For Summary
The discussion revolves around the dynamics of a hollow rod with a mass sliding inside it, focusing on angular and linear motion after an elastic impact. Key calculations involve determining the speed of the ball and the angular speed of the rod immediately after the impact, as well as the impulse of the constraint reaction. Following the impact, the motion of the mass inside the rod is analyzed to find its speed and the rod's angular speed when the mass reaches the end. The conversation also addresses the complexities of conservation laws, highlighting the importance of distinguishing between linear and angular momentum, and the implications of inelastic collisions on the system's overall motion. The problem is noted for its challenging nature, requiring careful application of physics principles.
  • #31
Delta2 said:
This looks good

You have to take the angular momentum around the CM of the system. And also the total moment of inertia around the CM of the system. I can't understand what the term ##I_{TOT}V_{CM_y}(R-x_{CM})## is about?
The terms is an error, i tought that ## R - x_{CM} ## was the radius of the circumference along which the system rotates.
I'm not understanding perfectly what you mean (probably because I'm a little dumb) but if i fix that term i got:
## -m_0 v_0 R = I_{TOT} V_{CM_y} (x_{CM}) + I_{TOT} \omega_{CM} ##
is it right?
 
Physics news on Phys.org
  • #32
To be honest i am not sure myself either at this point, i think the correct equation is $$-m_0v_0(R-x_{CM})=I_{TOT}\omega_{CM}$$, where ##I_{TOT}## the moment of inertia of the system around the CM.
 
  • #33
Delta2 said:
To be honest i am not sure myself either at this point, i think the correct equation is $$-m_0v_0(R-x_{CM})=I_{TOT}\omega_{CM}$$, where ##I_{TOT}## the moment of inertia of the system around the CM.
Ummm ok.
Is the total moment of inertia that I found in post 22 correct?
 
  • #34
Yes it is correct.
 
  • #35
Delta2 said:
Yes it is correct.
Ok thanks for your patience, but this problem was difficult as f*ck.
I hope this year the exam will be a little easier
 
  • Like
Likes Delta2
  • #36
Yes i agree, quite hard problem, testing to the extreme the understanding of concepts and principles.
Is it college level or university level exams this is from?
 
  • Like
Likes Lnewqban
  • #37
Delta2 said:
If we don't make this assumption, then a mini paradox will appear if we do the balance of the kinetic energy when the particle returns to A. Somehow the total kinetic energy will be increased (in point A , with regards to point B after the inelastic collision), and we won't be able to infer where this surplus "ghost" energy has come from.
Ah yes, it wouldn’t make it back to A if it were not elastic.
 
  • Like
Likes Delta2
  • #38
haruspex said:
Ah yes, it wouldn’t make it back to A if it were not elastic.
Thanks for resolving the paradox, if i tell you that i spend part of last night before sleep thinking where does the surplus of kinetic energy comes from you ll laugh with me won't you?
 
  • Like
Likes Lnewqban
  • #39
Delta2 said:
Yes i agree, quite hard problem, testing to the extreme the understanding of concepts and principles.
Is it college level or university level exams this is from?
University.
 
  • Like
Likes Delta2

Similar threads

Replies
13
Views
2K
  • · Replies 31 ·
2
Replies
31
Views
4K
Replies
3
Views
2K
Replies
11
Views
3K
Replies
10
Views
2K
  • · Replies 7 ·
Replies
7
Views
2K
  • · Replies 12 ·
Replies
12
Views
2K
  • · Replies 10 ·
Replies
10
Views
957
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 40 ·
2
Replies
40
Views
4K