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# PS DISTANCE PROBLEMS SPACE ROCKET

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Manager
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PS DISTANCE PROBLEMS SPACE ROCKET [#permalink]  19 Jun 2006, 06:41
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PLZ explain your reasoning and the equations used
OA IS 8OOOO

Two space rockets are launched. The first one with speed of 6000 mph was launched. The second one with speed of 8000 mph was launched 20 minutes later. Find the distance when they will be at equal distance from earth. Do not label your answer, it is already labeled for you.

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Manager
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Re: PS DISTANCE PROBLEMS SPACE ROCKET [#permalink]  19 Jun 2006, 06:50
8000
quote="mand-y"]PLZ explain your reasoning and the equations used
OA IS 8OOOO

Two space rockets are launched. The first one with speed of 6000 mph was launched. The second one with speed of 8000 mph was launched 20 minutes later. Find the distance when they will be at equal distance from earth. Do not label your answer, it is already labeled for you.

THANKS[/quote]
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Current Student
Joined: 29 Jan 2005
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6000X+2000=8000X

2000X=2000

X=1

8000*1= 8,000 miles

**Unless this problem involves air friction, cross winds, gravity, etc..
Director
Joined: 07 Jun 2006
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Anyway, breaking it down (more detail than MATT's simplicity :) )

we need distance travelled by A = distance by B

therefore, d1 = d2;
d1 = s1t1, d2 = s2t2,

Let them both meet after time 't'.

so d1 = 6000*(20/60)+6000*t -> distance travelled by rocket A
and d2 = 8000*t -> distance travelled by rocket B

so 2000 + 6000t = 8000t1 (time since leaving would be same when at equal distance)

so 2000 = 2000t => t = 1 hour, so distance is 8000*1 = 8000 miles.

The key here is to make that important conclusion - "let them both meet after time 't' and then use d = st.
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VP
Joined: 15 Jun 2006
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8000

How long did the 1st rocket travel in 20 min? 6000 kmh*1/3h=2000km
What's the differense in speeds of 2 rockets? 2000 km/h
Let's assume that 1st rocket stays still and the 2nd moves with the speed of 2000 kmh...
In this case 2nd rocket needs 1 hour (2000 km / 2000 kmh) to overtake the 1st rocket. How far did 2nd rocke travel in one hour? 8000 km.
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