What is the effective spring constant?

Question

anonymous · Answer

attachment

missmob · Answer

wats mainly the question the image or wat u wrote here

anonymous · Answer

The image is the diagram from which you have to calculate the effective spring constant, k_eff using k_1 and k_2.

missmob · Answer

If you have two springs of spring constants say K1 and K2, and if you connect these two in series the effective spring constant of the combination is given by ;
K = ( K1 * K2 ) / K1 + K2 ,
and when they are in parallel the effective spring constant is given by ;
K = K1 + K2 ;
one more thing you can have with you is that spring constant is inversely proportional to its length.

missmob · Answer

.....

anonymous · Answer

Yeah, I know that. I was trying it this way: the effective stretch in the spring shall be F/k2- 2F/k1 ('-' because the stretch of springs are in opposite directions)
So , net stretch= F*(k1-2k2)/k1*k2
So k_effective*net stretch=F (from second figure)
so k_eff= k1*k2/(k1-2k2)  But this answer is wrong apparently. I don't understand wherein I went wrong. Is it the negative sign?

anonymous · Answer

@missMob : Sorry for the late reply :P

missmob · Answer

wat u mean negative sign

anonymous · Answer

The negative sign between F/k2 and 2F/k1. Idk, I'm not too confident about my method.

missmob · Answer

lol im confused ask someone else please

espex · Answer

Perhaps I am under thinking this but if you look at direction alone:|dw:1372204195882:dw|