The $9$ kg block is then released and acceler$-$ ates to the right, toward the $5$ kg block. The surface is rough and the coefficient of friction between each block and the surface is $0\mathrm{.}4.$ The two blocks collide, stick together, and move to the right. Remember that the spring is not attached to the $9$ kg block. Find the speed of the $9$ kg block just before it collides with the $5$ kg block. Answer in units of m$/$s$.$