动量守恒定律告诉你,碰撞后速度是多少。

So the conservation of momentum tells you what the speed is after the collision.

youdao

若没有外力，作用于系统整体，在碰撞过程中，动量就是守恒的。

And if there is no net external force on the system as a whole during the collisions, then momentum is conserved.

youdao

我说我选择这个例子，它是完全弹性碰撞-，为0,Q, is, zero——，那么动能必然守恒。

I told you I chose the case of - a completely elastic collision — Q and so kinetic energy must be conserved.

youdao