Momentum is conserved, because there was no net external force, so now kinetic energy is also conserved.

动量是守恒的，因为它不受外力，因此动能也是守恒的。

youdao

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

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。

youdao

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

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。

youdao