A50-kilogram student threw a 0.40-kilogram ball with a speed of 20 meters per second. what was the magnitude of the impulse that the student exerted the ball?

By definition, the magnitude of the impulse is given by
 I = delta P
 where,
 delta P = variation of the linear amount of movement.
 P = m * v
 We have then:
 I = delta P
 I = delta m * v
 I = (0.40) * (20) - (0.40) * (0)
 I = 8 Kg * m / s
 
 the magnitude of the impulse that the student exerted the ball was
 I = 8 Kg * m / s

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.