Help with senior high school physics problem please?

[RickWinther]

http://sphotos-d.ak.fbcdn.net/hphotos-ak-snc6/s720x720/185062_10151033229627461_990741135_n.jpg [Broken]

You have these two springs hooked on to each other, hanging vertically from the ceiling, neither of them have any weight and both are hanging to the same object and we need somehow to come to the conclusion that are circled (1/D = 1/D1 + 1/D2)... If you don't have time to write the whole thing at least show me where to start cause I'm lost..
p.s. there's no wind either..

Sorry for my bad translation but I'm from Greece so I'm not sure of what terms you would use in English, but I think you'll get it as you're pretty much veterans most of you :)

ooops its in the wrong category, not really sure how to move if anybody could help me..

 

[nasu]

If the mass of the springs is neglected the elastic force should be same for each spring. What can you tell about the relationship between the total extension and the extension of each spring?

 

[RickWinther]

Well the only thing our teacher told us was that their normal lengths are not the same.. not really sure if it helps you

 

[nasu]

The question is if it helps you...
When you pull the bottom spring (by the weight attached there), the bottom goes down by some distance, let say x.
At the same time, each spring extends by some amount, let say x1 and x2.
What is the relationship between x, x1 and x2?
Once you realize this, you just need to write each extension in terms of the spring constant (and consider that the force is the same).

 

[RickWinther]

Aaaaa, I think i get it, so I will say:
Spring 1 extends by x1
Spring 2 x2
All in all x
So x1 + x2 = x
-F/D1 - F/D2 = -F/D
And then divide everything with -F ?
Or is this false?

 

[nasu]

This is it. It's OK.

 

[RickWinther]

Thanks! You're a lifesaver mate/sir