Answer:
the distance x increases as the student increase the mass of the cannon.
Explanation:
a) From the question ; we get to understand that for each launch, the students use a different mass which is launch at speed v relative to the ground.
This changes in the mass used brought about a change in the momentum at the same speed v ; perhaps an increase in momentum. However; since the conservation of the momentum is considered at each launching.
The momentum of the marble = momentum of the cannon
But since the momentum of the cannon increase ; therefore the same equivalent changes takes place in its kinetic energy . Therefore , the kinetic energy will increase and the distance will also increase in the bid to quench the amount of energy generated. Thus, the distance x increases as the student increase the mass of the cannon.
b)We all know that conservation of the momentum will definitely takes place after launching of the cannon.
Let assume that
is the momentum of the cannon with mass 
The kinetic energy of the canon will be:

Also the frictional force acting on the cannon is :

If the cannon move at an additional distance x; the frictional force acting at this area quench the amount of the energy generated and consume the kinetic energy of the cannon;
So;





Thus; it is consistent with the answer in (a) as increase in the mass of the marble will bring about an increase in distance x