A750-newton person stands in an elevator that is
accelerating downward. the upward force of the
elevator floor on the person must be
(1) equal to 0 n (3) equal to 750 n
(2) less than 750 n (4) greater than 750 n

When an elevator is accelerating downward, the normal force is equal to mg-ma (hence you feel a little lighter when accelerating downwards)

Therefore, the upward force of the elevator floor on the person must be less than 750N

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. 

Ai think hope that