Posted by amena on Sunday, May 29, 2011 at 9:13am.
A solid ball is released from rest and slides down a hillside that slopes downward at an angle 52.0 from the horizontal.What minimum value must the coefficient of static friction between the hill and ball surfaces have for no slipping to occur?

physics  drwls, Sunday, May 29, 2011 at 9:55am
Let u be the static friction foefficient.
Linear Acceleration = a
= M[g*sin52/M M*g cos52*u]/M
= g*[sin52  u cos52]
Angular acceleration = alpha = a/R
= g [sin52 ucos52)/R
(if there is no slipping)
= Ff*R/I < u*M*g*sin52*R/[(2/5)M R^2]
= (5/2)*u*g*sin52/R
Ff is the static friction force, which has a maximum value when slipping occurs.
To avoid slipping for a solid sphere, at that 52 degree slope angle,
(5/2)*u*g*sin52/R > g [sin52 ucos52)/R
g's and R's cancel.
u*[(5/2)sin52 + cos52] > sin 52
u > 1/[(5/2) + cot 52] = 0.305