Plz help with Physic questions.............ty?
2009-03-29 6:09 pm
A penny is placed on a rotating disc, which spins at 20 revolutions per minute. the diameter of the disc is 0.300m. what is the minimum coefficient of friction necessary to allow the penny to rotate if it is placed anywhere on the disc. ty
回答 (1)
2009-04-02 12:34 am
✔ 最佳答案
The centripetal force will be greatest when the penny is on the outer edge of the disc. This centripetal force must be supplied by friction. Thus Frictional force must be at least as big as the centripetal force: Thus,umg = mrω^2 where ω is the angular velocity in rad/s and u is the coefficient of static friction. Thus,
u = rω^2 / g where r = 0.15m , g = 9.8 m/s^2, ω = 20* 2π / 60 = 2.094 rad/s
Plug in the numbers and you will find u = .067
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