1. Nov 7, 2004

Flinthill84

problem with static friction and force

I have been working on this problem all weekend and I just can't get it!!

A small object is placed 10cm from the center of a phonograph turntable. It is observed to remain on the table when it rotates at 33 1/3 rev/min but slides off when it rotates at 45 rev/min. Between what limits must the coefficient of static friction between the object and the surface of the turntable lie? Calculate the value of Fc.

I believe I found the first part of the question by taking Us=v^2/g*r for each value that it rotates. I think that I need to use the formula Fc=m*v^2/r for the second part of the problem but I have no clue how to find the mass and have looked all through my notes and physics book. Please if you could help me I would greatly appreciate it.

Last edited: Nov 7, 2004
2. Nov 7, 2004

What is Fc ?

3. Nov 7, 2004

Flinthill84

I believe it is the force

4. Nov 7, 2004

Phymath

its centrip force

Last edited: Nov 7, 2004
5. Nov 7, 2004

Flinthill84

it is actually F sub c in the problem....centripetal force

6. Nov 7, 2004

7. Nov 7, 2004

Leong

are you allowed to write Fc in term of m?

8. Nov 7, 2004

Flinthill84

yeah I am pretty sure I am

9. Nov 7, 2004

Leong

then just go ahead with it. give the range of Fc using the range of your coefficient of static frictional.

10. Nov 7, 2004

Flinthill84

how do I go ahead with it?? I don't know the mass

11. Nov 9, 2004

Leong

i thought you said that you were allowed to write Fc in term of m ?

12. Nov 10, 2004

Leo32

Flinthill,

Just start working on the problem using a symbolical "m" for mass. If the figure is not in the original problem, this usually means it will cancel out somewhere.

Think of it as a nice aid to proove your solution: if the mass doesn't cancel out in your solution, you might be doing something wrong...

I usually only fill out the numbers once I have a general solution written out in symbols.

Greetz,
Leo