general question?

Question

i have the following info:

mass is .011 kg

radius is .12 m

period is 1.8 s/rev

Fn=.108

How do I calculate Ff with this info?

Answer 1

Pretty scanty information when you don't actually describe the problem. But I'll take a shot at it. A turntable is spinning with a period of 1.8s/rev, or an angular rate w = 3.49 rad/s. An object of 0.011 kg mass (normal force Fn=weight=0.108 N when g=9.82) just slides off the turntable when initially at a radius of 0.12 m. What is the friction force Ff?
When the object just slides off, the centripetal force = Ff. The centripetal force is m*w^2*r = 0.01608 N, so this is the Ff. Incidentally this means the coefficient of friction = 0.01608/0.108 = 0.1489