Collision and Spring Constant: Calculating Amplitude for a Mass-Spring System

[Yosty22]

Homework Statement

An 11.5kg mass is traveling to the right with a speed of 2.4m/s on a smooth horizontal surface when it collides with and sticks to a second 11.5 kg mass that is initially at rest but is attached to a light spring with force constant 110N/m.

Homework Equations

f=1/T
T=1/f
F=-kx
A=v*(sqrt(m/k))

The Attempt at a Solution

I tried to use the equation A=V*sqrt(m/k). I plugged in 2.4 m/s in for v, k is the force constant, 110N/m, and I used 23 kg for the mass (the two masses added together). Solving for this, I get 1.097m. However, this is incorrect.
Any ideas where I went wrong?

Also, in case it is necessary, I have already solved for the frequency: f=0.348 Hz.

 

[jldibble]

what exactly are we looking for? I don't see the original question.