When it comes to a ballistic pendulum, why would it be justified to say that the momentum in the horizontal direction is conserved over the collision interval?

I think it's because of the law of conservation of linear momentum, but I feel like there is more to it than that. Am I on the right track, and if I am, how do I elaborate on that?

1 answer

linear momentum is a vector, conservation of momentum is a vector law. It is as simple as that.