To solve this problem we will apply the concepts related to the conservation of kinetic energy and elastic potential energy. Thus we will have that the kinetic energy is

And the potential energy is

Here,
m = mass
v = Velocity
x = Displacement
k = Spring constant
There is equilibrium, then,
KE = PE

Our values are given as,

Replacing we have that


Therefore the speed of the cart is 2.19m/s