✔ 最佳答案
Let ff be the frictional force. Consider the rotational motion,
Ff x R = [MR^2/2] x (angular acceleration)where R is the disk radius, and M is the disk mass
But angular acceleration of the disk = a/R, where a is the linear acceleration if the disk rolls without slipping
hence, Ff x R = [MR^2/2]/(a/R)
u.Mgcos(30) x R = MR^2/2 x a/Rwhere u is the coefficient of friction and g is the acceleration due to gravitySimplifying, we have, ugcos(30) = a/2 ----------------- (1)Consider the linear motion,
Mg.sin(30) - Ff = Ma
i.e. Mg.sin(30) - uMgcos(30) = Ma
g.sin(30) - ugcos(30) = a
substituting value of a from (1)
g.sin(30) - ugcos(30) = 2ug.cos(30)
u = [tan(30)]/3 = 0.19