The 9 kg block is then released and accelerates to the right, toward the 5 kg block. The surface is rough and the coefficient of friction between each block and the surface is 0.4 . 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.