I suspect the change in momentum was exaggerated to fit the story.
You know like pretty much every thing ever shot for TV or film
, it has it's basis in reality (and is far closer than many*), but it's an adaptation of a short story that has to make the point in 30 seconds or so of screen time.
I vaguely remember reading the original short story (or one very like it) many years ago and it took place over a longer period of time.
*I mean she didn't have to keep throwing hands to keep her speed up, or keep accelerating once she threw it, the former is so annoyingly common in TV/Film about the only show I've ever seen that got it constantly right was B5 with the earth ships that had to turn around and do burns to slow, otherwise they'd keep coasting, which led to some great bits when they stopped using the main engines and used thrusters to change facing during fights).
But this episode looked like it was trying to be realistic. Anime doesn't do that.
You're probably watching the wrong anime
Try Planetes
It's in large part about the problems you face in space with regards to junk (at least the first half of the series) and the economics and necessity of cleaning it up, and for many years one of the more accurate portrayals of life in space and the issues you get with equipment that is probably largely achievable now.
Anime ranges from quite realistic to utter fantasy, it's just that the more realistic stuff doesn't tend to get big audiences outside of the odd film.
- no explanation given or needed.
