ak
see
googly from resnick in QOD
fine particles of a substance are to be stored in a heap on ahorizontly circular plate of radius a if the coefficient of static friction bw particles is k the maximum possible height is
A ak
B ak/2
C a/k
d ak2
http://targetiit.com/iit_jee_forum/posts/01_03_09_googly_from_resnick_3045.html
see in page 2 there
http://targetiit.com/iit_jee_forum/posts/2/01_03_09_googly_from_resnick_3045.html