Physics
posted by mymi .
A 21.0g metal cylinder is placed on a turntable, with its center 90 cm from the turntable's center. The coefficient of static friction between the cylinder and the turntable's surface is ìs = 0.84. A thin, massless string of length 90 cm connects the center of the turntable to the cylinder, and initially, the string has zero tension in it. Starting from rest, the turntable very slowly attains higher and higher angular velocities, but the turntable and the cylinder can be considered to have uniform circular motion at any instant. Calculate the tension in the string when the angular velocity of the turntable is 70 rpm (rotations per minute).

tension=mass*w^2 r
where
w in rad /sec 
Bob I have already tried that, but that does not give correct answer.A similar problem with different values have the following:
If the mass in this problem is 18 g and radius is 75 cm and mu s is 0.87 and angular velocity is 45 rpm then the tension is 0.146 N. I have no clue to get that answer, I have tried so many different ways all failed.