A spring $($k $=300$ N$/$m$)$ is placed in a vertical position with its lower end supported by a horizontal surface. A $3\mathrm{.}0-$kg block that is initially $0\mathrm{.}50$ m above the upper end of the spring is dropped from rest onto the spring. Using energy consideration, calculate the speed of the block at the instant it has fallen $0\mathrm{.}68$ m $($compressing the spring $0\mathrm{.}18$ m$.$ Ignore air resistance