Three masses lie on the x-axis. Object A is at the origin and has a mass of 199.1 kg. Object B has a mass of 592.9 kg and is located 7.5 meters in the positive x direction from A. Finally, object C, which has a mass of 330 kg, is positioned 4 meters from object B, so that object B is between objects A and C. What is the force acting on object A? (The sign of your answer will denote direction.) The force on A is _?

You need to be more specific.  i really don't know what a "motion map" is.you can draw a graph of an object's position, distance, displacement, speed,velocity, or acceleration versus time, or you can draw a graph of the object's x-position versus its y-position and not give any information about time at all.if the graph presents position or displacement against time,  then constant velocity is a straight line . . i.e. a line that has  constant slope.if the graph shows speed against time, then constant velocityis a horizontal piece of line.if the graph shows acceleration against time, then constant  velocity is a piece of line that lies on the x-axis . . it's value is zero. 

No. rocks can follow various pathways.