For the part a) we need only the momentum of the box and we have the data to find it.
Momentum is given by,
where clearly, p is the momentum, m the mass of the box and v is the velocity.
Substituting,
For part b) we need an analysis of the situation. We understand that the box on a surface that has no friction will continue to rotate at the same speed previously defined. The box can only stop with friction, so,
<em>It is the same that part a)</em>