Final answer:
To maintain constant horizontal speed, a force equal in magnitude but opposite in direction to any existing horizontal forces must be applied. In terms of drawing a free-body diagram with conflicting forces, one should depict the actual directions and magnitudes of the forces. Lastly, applying Newton's second law involves confirming that the units are consistent and the solution makes sense.
Step-by-step explanation:
The student's question involves understanding Newton's laws of motion, particularly how different forces interact to affect the motion of an object. When an object moves with a constant speed horizontally, it means there are no net horizontal forces acting on it due to Newton's first law. Thus, a force to the right would need to be exactly equal in magnitude but opposite in direction to the sum of all horizontal forces acting to the left. Considering the given forces, if we have a 2N force to the left and the objective is to keep the object moving with a constant speed horizontally, a 2N force would be required to the right, counterbalancing the existing leftward force (assuming no other horizontal forces are present).
Regarding the free-body diagram that represents a body pushed downward by a force of 5 units and upward by a force of 2 units, the correct representation would be option d: Two force vectors acting at a point, one pointing down with a length of 5 units and the other pointing up with a length of 2 units.
For applications of Newton's second law, Fnet x = ma, the net external force on an object equals the mass of the object multiplied by its acceleration. If the object does not accelerate, then the net force in that direction is zero. It's always important to check that the answer is reasonable and that the units used are correct.