Answer:
Explanation:
The magnitude of the change in momentum of block A is equal and opposite the magnitude of the change in momentum of block B.
According to law of conservation of momentum , there should not be any change in the momentum in the system .The system consists of A and B . So if some change in momentum has occurred in A , the other must have equal and opposite change in momentum so that they get cancel out and net change in momentum of system is zero.