Answer: C
One thing to note in this problem, is that there is a constant frictional force, meaning that the KE is not 100% conserved in comparison to the start of the problem.
In the top diagram, the KE is 1/2mv^2, however, in the diagram below, there is also a frictional force and 1/2(m1+m2)v^2
An expression for this can be:
Looking at the options available, the only correct answer is C.