Posted by phill on Tuesday, April 13, 2010 at 11:05pm.
A coin rests 15 cm away from the center of a turntable. The turntable starts to rotate at an angular acceleration of .8 rad/s^2 and after 7 seconds it slides off. What is the coefficient of static friction between the coin and the surface?
Just give me step by step on how to solve this problem.

physics  drwls, Wednesday, April 14, 2010 at 9:21am
It starts sliding when the static friction force reaches its maximum value. Its maximum value is Us*M*g.
Us is the static coefficeint you want to determine
After 7 seconds, the angular velocity is 5.6 rad/s and the centripetal acceleration is
Rw^2 = .15*(5.6)^2 = 4.7 m/s^2.
There is also continuing tangential acceleration of R*alpha = 0.12 m/s^2 The vectorsum acceleration is
4.701 m/s^2, so you can ignore the tangential acceleration effect.
Us*M*g = M R w^2
Us = R w^2/g = 4.7/9.8 = 0.48
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