An object moves along a distance MN. The first half of the block moves with a speed v1 = 30km/h. The second half of the way the object moves in two stages: in the first half, the object travels with a speed v2 = 20km/h, the second half goes at a speed v3 = 10km/h. Calculate the average speed of the object over the whole distance MN.

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One splits the atoms and molecules  the other combines them

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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.