- #1

shawli

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## Homework Statement

A light spring with constant k

_{1}is hung from an elevated support. From its lower end a second light spring is hung, which has spring constant k

_{2}. 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.

## Homework Equations

F= ma

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...