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One way to be sure that each person has constant velocity is to split the problem into two parts. The point of division is when person 1 A reaches the summit and turns around. If we set up a one-dimensional coordinate system as shown below, then during the first part of the problem person 1 is person A moves with velocity vA1 = + 5.0 m/s and person 2 moves with vB1 = + 2.0 m/s.