Which of Newton's laws of motion describes the motion of an object that has a net
force of ON?

Newton's first and second laws of motion both do, but I think the one you're looking for is: The First Law of Motion.  That description is a little more direct.

It says that if an object is not acted on by a net external force, then it continues in "constant, uniform motion".

answer; equivalent to a one(1) horsepower motor;

  distance on the y-axis and time on the x-axis.

explanation:

the instantaneous velocity = change in position/time taken

the slope of the graph should give instantaneous velocity.

  slope of a graph = change in value of y -axis / change in values of x -axis

  comparing both the equations

    change in value of y -axis = change in position

  change in values of x -axis = time taken

so position values should be on the y axis and time values should be on the x axis.

distance on the y-axis and time on the x-axis.