Can anyone help me with this problem? I've tried to do part a, but I don't think I'm doing it right.(adsbygoogle = window.adsbygoogle || []).push({});

A coin of mass 0.0050 kg is placed on a horizontal disk at a distance of 0.14 m from the center. The disk rotates at a constant rate in a counterclockwise direction. The coin does not slip, and the time it takes for the coin to make a complete revolution is 1.5 s.

a.) The rate of rotation of the disk is gradually increased. The coefficient of static friction between the coin and the disk is 0.50. Determine the linear speed of the coin when it just begins to slip.

FN - Fg - Ff = ma

(FN = mg?)

mg - mg - u(mg) = (mv^2)/r

(.5)(9.8) = (v^2)/.14

v = .83 m/s

b.) If the experiment in part a were repeated with a second, identical coin glued to the top of the first coin, how would this affect the answer to part a? Explain your reasoning.

It would have no effect because the mass cancels out.

Thanks!!

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Circular Motion and Friction of a coin

**Physics Forums | Science Articles, Homework Help, Discussion**