Problem

A block of mass

m

is placed at rest on a horizontal rough surface with angle of friction

\phi

. The block is pulled with a force

F

at an angle

\theta

with the horizontal. The minimum value of

F

required to move the block is a.

\frac{mg \sin \phi}{\cos(\theta - \phi)}

\frac{mg \cos \phi}{\cos(\theta - \phi)}

mg \tan \phi

mg \sin \phi