A block is fastened to a horizontal spring. The block is pulled to a distance x=10 cm from its equilibrium position (at x=0 ) on a frictionless…

A block is fastened to a horizontal spring. The block is pulled to a distance $\displaystyle x=10 \mathrm{~cm}$ from its equilibrium position (at $\displaystyle x=0$ ) on a frictionless surface from rest. The energy of the block at $\displaystyle x=5$ cm is $\displaystyle 0.25$ J. The spring constant of the spring is $\displaystyle \_\_\_\_$ $\displaystyle \mathrm{Nm}^{-1}$.