A box at rest is in a state of equilibrium half way up on a ramp. The ramp has an incline of 42° . What is the force of static friction acting on the box if box has a gravitational force of 112.1 N ?

Because the box is at rest, static friction balances the component of gravity pulling it down the ramp. That component is 112.1 N × sin(42°) ≈ 75 N. Therefore, the static friction force is 75 N, choice C.

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