Answer: C) 48 N forward
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Explanation:
Subtract the two forces, since they are working opposite one another.
79-31 = 48
The net force is 48 newtons forward. The truck is moving forward since the engine's force (79 N) is larger than the force of friction (31 N).
The force of friction cannot exceed the engine's force because friction only slows down an object, and does not push the object backward. In other words, if the object was stationary, then the ground isn't pushing the object backwards assuming you're on a level flat ground.
