We know that the momentum keeps constant in a inelastic collisions, so the product of mass and speed do not change: 
 m1 * v1 + m2 * v2 = m * v 
 1 * 1 + 5 * 0 = (1 + 5) * v 
 1 = 6 * v 
 v = 1/6 m/s 
 So the final speed of the 6 kg chunk will travel at 0.167 m/s