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33.
At 40o, the 5.00 kg box starts to slide from a stationary position.

Calculate the force friction.

A.     24.1 N                C.    37.5 N

B.     31.5 N                D.     49.0 N
    
Coefficient of static friction = Tan (theta) where theta is the angle when the objects starts to slide.  The coefficient of static friction is always greater than the coefficient of kinetic friction.

Tan 40o = 0.839

Ffriction = Coefficient of Friction x Forcenormal

Fnormal = mg x Cos 40o

Ffriction = 0.839 x 5.00 kg x 9.80 m/s2 Cos 40o = 31.5 N

The Correct Answer is B.