A custom-designed spring has a restoring force (x)=−(x+x2) F ( x ) = − ( α x + β x 2 ) where x x is the stretch from its equilibrium length, = α = 2.3 N/m, and = β = 3.6 N/m2. A 9-kg gizmo is attached to this spring and stretched 1.2 m over a frictionless, horizontal surface. If the gizmo is released from rest, how fast will it be moving when it passes as its equilibrium position?