It's That Time Again...

2008-11-16 12:04:07

#1

aj0404: It'll just be our little secret; +298|6797|Iowa...

i know you all love it (especially you FM).

https://img73.imageshack.us/img73/5986/arghud9.jpg

the question is very simple this time though. why in the hell is the answer to 3a 5626!? i know the issue has to be something to do with the radius because i missed 3c as well.

Given:

Earth Mass=5.58*10^24 kg
Earth Radius=6.37*10^6 m
v=(GM/r)^1/2

every time i work this out i get 5405 m/s. something is throwing me off on this problem and because of it every other problem i do is off by 10% as well. as usual karmaz will be given for help.

2008-11-16 12:06:24

#2

Flaming_Maniac: prince of insufficient light; +2,490|7154|67.222.138.85

You are supposed to use 2x the radius of the earth correct?

2008-11-16 12:11:43

#3

aj0404: It'll just be our little secret; +298|6797|Iowa...

yes.

2008-11-16 12:22:56

#4

Bevo: Nah; +718|6968|Austin, Texas

Flaming_Maniac wrote:
You are supposed to use 2x the radius of the earth correct?

r^2.

V=(GM/r)^1/2 is = to V = GM/r^2, no?

2008-11-16 12:27:14

#5

aj0404: It'll just be our little secret; +298|6797|Iowa...

he was referring to the fact that since the object is one earth radius above the earth you have to take it x2.

2008-11-16 12:38:17

#6

Babb Master Flash: Justice for the 96!; +540|6829|Oslo, Norway

Are you cheating???

2008-11-16 12:41:27

#7

aj0404: It'll just be our little secret; +298|6797|Iowa...

no, this is just an assignment. he'll re-open it for you if you can't get it but that doesn't really do any good because he doesn't teach anything. i'd rather come here and figure out how to do it so i don't fail the test.

2008-11-16 12:49:43

#8

Flaming_Maniac: prince of insufficient light; +2,490|7154|67.222.138.85

If you were using 2r I'm not really sure what you could be doing wrong, assuming your equations are correct.

Verify you are using the correct radius and mass?

2008-11-16 13:02:35

#9

aj0404: It'll just be our little secret; +298|6797|Iowa...

i am.

i guess i'll just assume the teacher screwed up the assignment...

2008-11-16 13:04:24

#10

Bevo: Nah; +718|6968|Austin, Texas

Work the problem backwards with that answer to find the radius that it's "supposed" to be?

2008-11-16 13:09:26

#11

aj0404: It'll just be our little secret; +298|6797|Iowa...

already tried it, that doesn't work either...

2008-11-16 14:55:10

#12

Airwolf: Latter Alcoholic; +287|7167|Scotland

that's high school stuff no? try this

https://img91.imageshack.us/my.php?image=astronomyuz2.png

2008-11-16 15:01:15

#13

Snake: Missing, Presumed Dead; +1,046|7013|England

aj0404 wrote:
i know you all love it (especially you FM).

http://img73.imageshack.us/img73/5986/arghud9.jpg

the question is very simple this time though. why in the hell is the answer to 3a 5626!? i know the issue has to be something to do with the radius because i missed 3c as well.

Given:

Earth Mass=5.58*10^24 kg
Earth Radius=6.37*10^6 m
v=(GM/r)^1/2

every time i work this out i get 5405 m/s. something is throwing me off on this problem and because of it every other problem i do is off by 10% as well. as usual karmaz will be given for help.

Well, I make the answer to 3a as 6242ms-1, but then if you have been told the correct answer is 5626, then ill shutup (that did involve changing the radius, btw)

2008-11-16 15:02:40

#14

Flaming_Maniac: prince of insufficient light; +2,490|7154|67.222.138.85

Airwolf wrote:
that's high school stuff no? try this

http://img91.imageshack.us/my.php?image … omyuz2.png

I'm sure they are doing Kepler if they haven't already.

2008-11-16 16:02:20

#15

DrunkFace: Germans did 911; +427|7129|Disaster Free Zone

MadKatter wrote:
Flaming_Maniac wrote:
You are supposed to use 2x the radius of the earth correct?
r^2.

V=(GM/r)^1/2 is = to V = GM/r^2, no?

No.

x^1/2 = sqrt x

1/x² = x^-2

Been too long since year 10 physics... So I can't help any more hen that.

2008-11-16 16:04:55

#16

phishman420: Banned; +821|6129

For some reason, every time I look at this thread, I think of Christmas.

2008-11-16 18:41:07

#17

aj0404: It'll just be our little secret; +298|6797|Iowa...

Snake wrote:
Well, I make the answer to 3a as 6242ms-1, but then if you have been told the correct answer is 5626, then ill shutup (that did involve changing the radius, btw)

eh?how did you get that?

phishman420 wrote:
For some reason, every time I look at this thread, I think of Christmas.

must be the sig.

2008-11-17 14:06:58

#18

Snake: Missing, Presumed Dead; +1,046|7013|England

aj0404 wrote:
Snake wrote:
Well, I make the answer to 3a as 6242ms-1, but then if you have been told the correct answer is 5626, then ill shutup (that did involve changing the radius, btw)
eh?how did you get that?

Scratch that, I took the distance to the satellite as 1.5x the radius of the Earth, thinking it was a diameter (yeah yeah, 11PM isnt the best time to be trying that shit ).

V = SQRT ( (6.67x10^-11 x 5.58x10²⁴) / (2 x 6.37x10⁶ ) )
V = 5405ms^-1

I agree with your answer, but if your teacher is right, then it is in the radius, because using his/her answer of 5626, and working it back, the radius calculation from centre to centre is 1.846x Earths radius, not 2x. It might have something to do with the line "Earths Mean Radius", but I cannot see how that would make any difference here.

But, using the 1.846 answer, 3C comes out to 1935 if that is correct?

Always hated those online tests, we always found errors in them.

BF2S Forums It's That Time Again...

Flaming_Maniac wrote:

aj0404 wrote:

Airwolf wrote:

MadKatter wrote:

Flaming_Maniac wrote:

Snake wrote:

phishman420 wrote:

aj0404 wrote:

Snake wrote:

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