In an out of control ceramics workshop, two clay balls collide in mid air and stick together. the first has mass 3.1 kg and collides with a second that is initially at rest. the composite system moves with a speed equal to one-third the original speed of the 3.1 kg ball. what is the mass of the second sphere?

We know that the first ball has a mass of 3.1 kg and moves at speed called V1 The second ball has a mass of M2 unknown and the both together moves a speed equal to V = V1/3

   The momentum keeps constant before and after balls collide, so:
 M1*V1 + M2*V2 = M*V
 3.1*V1 + M2*0 = (3.1+M2)*V1/3
 3.1*V1 = 3.1/3*V1+M2*V1/3
 3.1*V1-3.1/3*V1 = M2*V1/3
 (3.1-3.1/3)*V1 = M2*V1/3
 2*3.1/3 = M2/3
 M2 = 6.2
   Then the mass of the second ball is 6.2 kg

It indicates no change in temperature and the process of matter changing its state

Gas will most likely  fill the container