A net force xf acts on an object. what does this mean?

Answer: 6 - for an object to accelerate, Newton's law #2 tells us there must be a force acting on it. F=ma the effect of a force is to accelerate the mass. It cannot be 1, because the force must be centripetal to move the object in a circle. it can't be 2 because if an object is accelerating the velocity cannot be constant as it is moving faster. It can't be 3 because a stationary object has a net force of 0. 4 has nothing to do with the question. 5 - no force is needed for uniform motion. 7 - that is impossible.