A 50-Kg Crate Is Resting on a Horizontal Plank

Multiple Choice

A 5.0-kg crate is resting on a horizontal plank. The coefficient of static friction is 0.50 and the coefficient of kinetic friction is 0.40. After one end of the plank is raised so the plank makes an angle of 30 with the horizontal, the force of friction is:

A) 0
B) 18 N
C) 21 N
D) 22 N
E) 44 N