What is the velocity of an oscillator at a specific position?

[Capncanada]

Homework Statement

A simple harmonic oscillator has spring constant k = 7.8 N/m, amplitude A = 12 cm, and maximum speed 4.3 m/s.
What's the oscillator's speed when it's at x = 5.4 cm?

Homework Equations

KE_max=1/2*k*A^2
KE=1/2mv^2
ma=-kx
v=k/ma

The Attempt at a Solution

I used each equation in order to find the K_max, the mass of the oscilator, the acceleration, and then the velocity in that order, but the answer I got was wrong.

 

[jbsteele]

K_max=1/2(7.8N/m)(0.12m)^2= 0.00588Jm=KE_max/1/2v^2= 0.00588J/1/2(4.3m/s)^2= 0.000368kga=-kx/m=-7.8N/m(0.054m)/0.000368kg=-2080m/s^2v=k/ma=7.8N/m/(-2080m/s^2)= -0.003764m/s