Answer:
    v = √k/m   x
Explanation:
We can solve this exercise using the energy conservation relationships
starting point. Fully compressed spring
    Em₀ = [tex]K_{e}[/tex] = ½ k x²
final point. Cart after leaving the spring
    [tex]Em_{f}[/tex] = K = ½ m v²
    Em₀ = Em_{f}
    ½ k x² = ½ m v²
    v = √k/m   x