Find the frequency of the cylinder's vertical vibration

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Homework Help Overview

The discussion revolves around determining the frequency of vertical vibrations of a cylinder connected to a spring and pulley system. Participants are exploring the relationships between the spring constant, mass, and displacement in the context of harmonic motion.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning, Assumption checking

Approaches and Questions Raised

  • The original poster attempts to derive the frequency using equations related to angular frequency and period but expresses uncertainty about the impact of the spring and pulley on their calculations. Other participants inquire about the visibility of the figure and clarify the setup, while also discussing the relationship between the displacement of the spring and the cylinder.

Discussion Status

The discussion is active, with participants providing clarifications and questioning assumptions about the system's setup. Some guidance has been offered regarding the relationship between the displacements of the spring and cylinder, but no consensus has been reached on the original poster's calculations.

Contextual Notes

Participants are working with a specific setup involving a spring, pulley, and cylinder, and there are indications of missing information regarding the figure that illustrates the problem. The inherent properties of the spring constant are also under discussion, with emphasis on how they relate to the problem at hand.

CGI
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Homework Statement


upload_2016-2-20_14-47-16.png

upload_2016-2-20_14-47-30.png


Homework Equations



w = √k/m
w = 2π/P
ƒ = 1/P

The Attempt at a Solution


I feel like I'm so close to the answer, I think it has something to do with the fact that there's a spring and pulley in the system that is throwing my answer off. I have

√k/m = 2π/P

So,

P = 2π(√m/k) Then we take the number one and divide it by P to find frequency

1/2π(√m/k) which I get to be

ƒ = √(k/m) / 2π, which is close, but not quite. The answer is actually

ƒ = √(k/m)/(4π)

Can anyone help me understand where I'm going wrong? Thank you! :)
 

Attachments

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Can you repost the figure so that the entire figure is visible?
 
I'm not sure what you mean. The cylinder, pulley and spring is the entire figure. Or is the picture not visible?
 
The picture is visible, but I can't tell what is at the bottom end of the string on the right side.
Edit: OK, I thought there was more to it. The string is fixed at the lower right. Sorry, I get it now.
 
Oh, I believe the bottom of the string is attached to a fixed end.
 
CGI said:
Oh, I believe the bottom of the string is attached to a fixed end.
Thanks.
 
If the spring stretches by an amount Δx, what is the vertical displacement Δy of the cylinder?
 
Would Δy = 1/2Δx?
 
Yes. No, but you have the right idea.
 
  • #10
Okay,but how exactly would the change in displacement affect the frequency? Would the displacement affect the value of K? Therefore, changing our ω?
 
  • #11
No, the spring constant is an inherent property of the spring. k is not affected by displacements of the spring or cylinder. I spoke too soon in post 9 where I first agreed with your answer in post 8. Do you see the correct relation between Δy of the cylinder and Δx of the spring?

Next, you might consider the situation where the cylinder is hanging at rest. What is the tension in the string? What is the force of the spring? How much is the spring stretched when the cylinder is hanging at rest?
 

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