A person walks first at a constant speed of 2 m/s along a straight line from point A to point B and then back along the line from B to A at a constant speed of 4 m/s. What is the average speed (in m/s) over the entire trip? Select one:
a. 2.67
b. 1.33
c. 5.33
d. 2.00
e. zero

acceleration = (change in speed) / (time for the change)

change in speed = (20-120)= -100 m/s.

1.5 min = 90 sec

acceleration = -100/90 = -1.11 m/s^2.

we don't care about the 150kg or the 2,500 meters. they don't make any difference.

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i am pretty sure it is c because when people are closer together, they cannot move as freely. picture being in a mostly full elevator, for instance. the people are right next to you, and you can barely move.