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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the ima (higher than 1m) will be greater than the ima with the height of 1m.