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
The OA is D.
Please, can anyone explain this PS question for me? I can't get the correct answer. Thanks.
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A rocket soars for 12 seconds at 150 meters per second.
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Jake@ThePrincetonReview
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The key to this problem is to use the formula: Distance = Rate x Time.
Step 1: Find the total distance the rocket has traveled.
Part I: Rocket goes up: The rocket soars for 12 seconds (time) at 150 meters per second (rate).
D = R x T
D = 150 m/s x 12 s
D = 1800 meters
Part II: Rocket comes down: Distance = 600 meters, Time = 3 seconds
Therefore, the total distance the rocket has traveled is 1800 + 600 = 2400 meters
Step 2: Find total time the rocket has traveled: 12 + 3 = 15 seconds
Step 3: Use D = R x T to find the rocket's speed (rate)
2400 = R x 15
R = 2400/15
R = 160
Hope that helps!
Step 1: Find the total distance the rocket has traveled.
Part I: Rocket goes up: The rocket soars for 12 seconds (time) at 150 meters per second (rate).
D = R x T
D = 150 m/s x 12 s
D = 1800 meters
Part II: Rocket comes down: Distance = 600 meters, Time = 3 seconds
Therefore, the total distance the rocket has traveled is 1800 + 600 = 2400 meters
Step 2: Find total time the rocket has traveled: 12 + 3 = 15 seconds
Step 3: Use D = R x T to find the rocket's speed (rate)
2400 = R x 15
R = 2400/15
R = 160
Hope that helps!
Jake Schiff
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Alternate approach: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
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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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
Average speed = total distance/total time
The soaring distance is 12 x 150 = 1800 meters, and the time is 12 seconds.
The plummeting distance is 600 meters, and the time is 3 seconds.
Average speed = (1800 + 600)/(12 + 3)
Average speed = 2400/15 = 160
Answer: D
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