A light spring with constant k1 is hung from an elevated support. From its lower end a second light spring is hung, which has spring constant k2. An object of mass m is hung at rest from the lower end of the second spring.
a) Find the total extension distance of the pair of the springs.
Fs = kx
The Attempt at a Solution
I treated the two springs as a single device and made the following equation for the forces acting on the mass:
Fnet = 0
Fs1 + Fs2 - mg = 0
k1x + k2x = mg
(k1 + k2)x = mg
x = mg/(k1 + k2)
But this answer is incorrect. (Correct answer: x = mg(1/k1 + 1/k2).
Would someone be able to clarify what is happening in this system? I seem to be missing something...