Problem in a circular motion (find the max Frequency)

  • #1
Member advised to use the homework template for posts in the homework sections of PF.
In the figure below we put a small coin on a disc, which rotates at constant frequency f, at a distance D=0.2m by the disc rotation axis. If the coefficient of friction is μ=0.5, then what is is the maximum frequency that can have the disc so that the currency does not slip? g=10 m/sec^2

Anyone could help me how to start? I know that i can take Fk=Ts=m*v^2/D and replace the velocity with v=2πDf but i dont know the mass.. am i on the right way? Ts=static friction
 

Attachments

  • 14686180_967343080042526_1138366334_n.jpg
    14686180_967343080042526_1138366334_n.jpg
    39.3 KB · Views: 317
  • 14741594_967344550042379_2108361043_n.jpg
    14741594_967344550042379_2108361043_n.jpg
    15.4 KB · Views: 265
Last edited:

Answers and Replies

  • #2
kuruman
Science Advisor
Homework Helper
Insights Author
Gold Member
10,263
3,391
You are on the right track. Call the mass "m" and proceed with the algebraic solution. Maybe you will discover that you don't need the mass after all.

Also, I don't know what Fk=Ts=v^2/D is all about, but it does not look correct.
 
  • #3
its the centripetal force my mistake, Fc=m*v^2/D which equals to static friction if i am correct.
 
  • #4
kuruman
Science Advisor
Homework Helper
Insights Author
Gold Member
10,263
3,391
You are correct. As the speed increases, the force of static friction has to increase to keep the coin going around in the circle. Can the force of static friction increase indefinitely?
 
  • #5
haruspex
Science Advisor
Homework Helper
Insights Author
Gold Member
2020 Award
36,212
6,830
@kuruman, do any of the offered answers look right to you? I get the reciprocal of one of them.
 
  • #8
kuruman
Science Advisor
Homework Helper
Insights Author
Gold Member
10,263
3,391
@kuruman, do any of the offered answers look right to you? I get the reciprocal of one of them.
None of the answers look right to me and I too get the reciprocal of one of them.
 
  • #9
I'm saying that static friction equals to maximum friction, also the static friction equals to centripetal force. So i have Ts=Fc=m*v^2/D and Tmax=μ*Ν (N=weight)..
If you replace the speed in the first equation you get Ts=4π²Df²m.. So my equation is: μN=4π²Df²m =>μ*m*g=4π²Df²m.. if i solve this for f and replace the numbers, i know i get fmax=5/2π.. what am i doing wrong then?
 
  • #10
kuruman
Science Advisor
Homework Helper
Insights Author
Gold Member
10,263
3,391
I also get 5/(2π). Are we both wrong in exactly the same way or is the correct answer missing from the list that you are given?
 
  • #11
no its not.. anyway I will wait until the tuesday.. thanks both of you guys
 
  • #12
haruspex
Science Advisor
Homework Helper
Insights Author
Gold Member
2020 Award
36,212
6,830

Related Threads on Problem in a circular motion (find the max Frequency)

Replies
5
Views
2K
Replies
5
Views
3K
  • Last Post
Replies
4
Views
2K
  • Last Post
Replies
6
Views
5K
Replies
1
Views
4K
  • Last Post
Replies
3
Views
2K
  • Last Post
Replies
1
Views
6K
Replies
3
Views
2K
  • Last Post
Replies
18
Views
755
Top