A Block of Mass M Is Held Motionless on a Frictionless

Multiple Choice

A block of mass M is held motionless on a frictionless inclined plane by means of a string attached to a vertical wall as shown in the drawing.
-Assume the plane is not frictionless and the string breaks, what minimum value of the coefficient of static friction, $\mu$ _s, would prevent the block from sliding down the inclined plane?

A) zero
B) 1
C) cos $\theta$
D) sin $\theta$
E) tan $\theta$