Answer:
4 kg m/s (option B)
Step-by-step explanation:
We use conservation of momentum to solve this problem.
In the initial state, the ball has momentum zero (no momentum), and the bat has a momentum of 12 kg m/s.
Since the momentum of the system that interacts ("bat plus ball"), has to be conserved (that means the final total momentum must equal the initial total momentum), we have:
Total initial momentum = 0 kg m/s + 12 kg m/s = 12 kg m/s
Total final momentum = 8 kg m/s + X
where X is our unknown: the final momentum of the bat, and 8 kg m/s is the final momentum of the ball.
We make these two quantities equal since the total momentum has to e conserved, and solve for the unknown X in the equation:
Total initial momentum = Total final momentum
12 kg m/s = 8 kg m/s + X
12 kg m/s - 8 kg m/s = X
X = 4 kg m/s