Answer
C, A, B.
Work Step by Step
Momentum is conserved in these collisions. Calculate the total momentum before the collision, which equals the momentum afterward. The larger the final momentum, the larger the speed.
The momentum in each situation is calculated here:
$$(5M)(4 m/s) + 0 = 20M \frac{kg \cdot m}{s}$$
$$(5M)(4 m/s) + (M)(-1 m/s)= 19M \frac{kg \cdot m}{s}$$
$$(5M)(5 m/s) + (M)(-2 m/s)= 23M \frac{kg \cdot m}{s}$$
