Cart A with a mass equal to 24 kg is moving to the right at 3.2 m/s. It collides with Cart B that has a mass of 32 kg and is moving to the left with a velocity of 12.8 m/s. After the collision,
Cart A has a velocity of 2.9 meters per second to the left. What is the speed of the Cart B after
the collision?

Explanation:

According to the Law of Momentum Conservation, what happens after the collision has to equal what happened before the collision because momentum cannot be created nor destroyed; it has to go somewhere else. Like energy eventually dissipates into heat. The equation for this is:

and filling in our info, calling right positive and left negative:

[(24(3.2) + 32(-12.8)] = [(24(-2.9) + 32(vB)] and

[(77 - 410)] = [(-7.0 × 10¹ + 32vB)] and

-330 = -7.0 × 10¹ + 32vB and

-260 = 32vB so

vB = -8.1 m/s Thus, cart B is moving to the left at a velocity of 8.1 m/s

(I used the rules for sig dig very intentionally and correctly; I'm not sure how strict your teacher is about them. I require my students to use the rules to perfection, as I did here.)