A block of mass $m=0.1\;kg$ is connected to
a spring of unknown spring constant k. It
is compressed to a distance x from its
equilibrium position and released from rest.
After approaching half the distance $\bigg(\large\frac{x}{2} \bigg)$
from equilibrium position, it hits another
block and comes to rest momentarily, while
the other block moves with a velocity
$3 ms^{-1}$. The total initial energy of the spring is :
