What is the correct radius for spinning a rope with mass?

  • Thread starter Thread starter Panphobia
  • Start date Start date
  • Tags Tags
    Mass Rope
Click For Summary

Homework Help Overview

The discussion revolves around a physics problem related to the motion of a mass attached to a rope, specifically focusing on the correct interpretation of the radius in the context of circular motion and pendulum dynamics.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants explore the relationship between the radius of motion and the length of the rope, questioning whether the radius should be adjusted based on the angle of the rope. There is also a discussion about the distinction between circular motion and pendulum motion.

Discussion Status

The conversation has seen participants clarifying their understanding of the problem, with some expressing confusion about the setup. There is acknowledgment of the pendulum nature of the motion, and participants are working through the implications of this on the radius used in calculations.

Contextual Notes

Some participants reference specific angles and the positioning of axes, indicating that assumptions about the motion's nature may have led to initial misunderstandings. The original poster's urgency due to an upcoming midterm is also noted.

Panphobia
Messages
435
Reaction score
13

Homework Statement



nlsmts.png


Homework Equations



mv^2/r
v^2/r

The Attempt at a Solution


My physics midterm is tomorrow and I was doing review today, so I did this question, then looked at the professor's solutions. For the radius in both equations he used the length of the rope, but shouldn't the radius be Lsin20? Also the way he positioned his y and x-axis was that the Y axis was parallel to tension(EXTRA INFO).
 
Physics news on Phys.org
Hi Panphobia! :smile:

(your professor can't spell "vertical"! :wink:)
Panphobia said:
For the radius in both equations he used the length of the rope, but shouldn't the radius be Lsin20? Also the way he positioned his y and x-axis was that the Y axis was parallel to tension(EXTRA INFO).

I think you're misunderstanding "swings in a vertical circle".

It means that the circle is in a vertical plane. :wink:

(Lsin20° would be for a horizontal circle)
 
Yea that is what I meant, it is pointing down. So is my professor wrong? OHHHH CRAPP didn't know it was a pendulum, sorry man this question was dumb :(
 
no, the ball is moving in the plane of the paper, and so the radius of the circle is L :confused:
 
Yea I pointed out earlier that it is moving as a pendulum and not in a circle.
 
if the radius of the circle is L, why would you use Lsin20° ? :confused:
 
I figured that out earlier, I thought original that it the mass was spinning about the vertical axis at angle theta, THEN the radius would be from the end of the mass to the vertical axis. But later I read the question more in depth and found that it was a pendulum, and if it is a pendulum then the radius is the length of the rope.
 
(isn't that what i said? :confused:)

so is it all ok now? :smile:
 
  • Like
Likes   Reactions: 1 person
Yes thank you for your help!
 

Similar threads

  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 18 ·
Replies
18
Views
2K
  • · Replies 39 ·
2
Replies
39
Views
7K
  • · Replies 13 ·
Replies
13
Views
3K
  • · Replies 10 ·
Replies
10
Views
3K
  • · Replies 22 ·
Replies
22
Views
7K
  • · Replies 3 ·
Replies
3
Views
2K
Replies
12
Views
2K
  • · Replies 4 ·
Replies
4
Views
1K
Replies
11
Views
3K