swerve wrote:A rocket soars for 12 seconds at 150 meters per second. It then plummets 600 meters in 3 seconds. What is the average speed of the rocket in meters per second?
A. 140
B. 150
C. 155
D. 160
E. 175
Alternate approach:
Lower rate = rate upward = 150 meters per second.
Higher rate = rate downward = d/t = 600/3 = 200 meters per second.
Since the rocket travels 12 seconds upward and 3 seconds downward, the time ratio for the two rates = (12 seconds) : (3 seconds) = 4:1.
Implication:
Of every 5 seconds, 4 seconds are traveled at 150 meters per second, and 1 second is traveled at 200 meters per second.
Thus, the average rate for every 5-second interval = (4*150 + 1*200)/5 = 800/5 = 160.
The correct answer is
D.
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