SOLUTION: A rocket was fired up at a speed of 5000km/h. but after going up 10 km , it fell back at the speed of 200 km/h . what was its average speed over the round trip ?

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Question 203885: A rocket was fired up at a speed of 5000km/h. but after going up 10 km , it fell back at the speed of 200 km/h . what was its average speed over the round trip ?
Found 2 solutions by Alan3354, MathTherapy:
Answer by Alan3354(69443) About Me  (Show Source):
You can put this solution on YOUR website!
A rocket was fired up at a speed of 5000km/h. but after going up 10 km , it fell back at the speed of 200 km/h . what was its average speed over the round trip ?
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Did it go up at a constant speed of 5000 khp, then immediately reverse and descend at 200 kph? Did it start at 5000 kph, or was that the speed it reached as its engine burned?

Answer by MathTherapy(10549) About Me  (Show Source):
You can put this solution on YOUR website!

D = ST ; S = D/T ; T = D/S

Since the rocket’s speed upward was 5,000km/h for 10 km, then its time to make the journey upward was 10%2F5000, or 1%2F500hr.

Since on its journey downward the rocket traveled at 200km/h for the same 10 km, then its time to make the journey downward was 10%2F200, or 1%2F20hr.

Now, since the rocket traveled a total of 20 km, and its time over that period was %281%2F500%29%2B%281%2F20%29 = 26%2F500 = 13%2F250, its average speed for the entire journey is: 20%2F%2813%2F250%29

20%2F%2813%2F250%29 = %2820%2F1%29%2A%28250%2F13%29, or 5000%2F13 = highlight_green%28384.6154%29 km/h