The boat will keep moving

船将继续运动
because there's no force on the boat; it's going to keep moving.

因为船不受任何外力作用它将继续运动
The question is, "How come I suddenly have momentum in my system

问题是这个系统为什么突然具有了动量
when I had no momentum before?"

而在初始状态时系统没有动量
It's because the F external has now come into play.

这就是因为外力 F 的作用
Previously, it was just you and the boat

一开始你和船构成一个系统
and you couldn't change your total momentum.

整体的动量不能改变
But the ground is now pushing you,

但是现在大地给你一个推力
and it's obviously pushing you to the right

显然方向是向右的
because you were flying to the left and you were stopped.

因为它阻止了你向左的飞行
So, your combined system, you and the boat,

所以整个系统你和船这个整体
have a rightward force

受到了一个向右的力