If we accept system as a summation of rocket+gas, total force must be zero. Action-reaction is between rocket and gas. So if we want to know about force that affected to rocket, we must apply this rule with selecting only rocket as a control volume.
For the momentum of the system at time equals t, why do we assume there was no propellant that already got ejected (and therefore had its own momentum to contribute to the system momentum) prior to that time t?
![Lp. Сердце Вселенной #60 РОЖДЕНИЕ ЛОЛОЛОШКИ [Финал] • Майнкрафт](http://i.ytimg.com/vi/YoR0pAV9FVQ/mqdefault.jpg)
He keeps using different colored markers, but they're all the same color. Insane.
How...how does he write backwards like that?? Is there a trick, or is he just amazing at it?
There is a trick to it. Check out lightboard.info/ to see how it is done (and how you can make your own). :)
MIT OpenCourseWare Ah, it's a mirror image, right, that makes sense!
The clue is that he's writing with his left hand and starts on the top right of the board
If we accept system as a summation of rocket+gas, total force must be zero. Action-reaction is between rocket and gas. So if we want to know about force that affected to rocket, we must apply this rule with selecting only rocket as a control volume.
Great mirror writing skills!
For the momentum of the system at time equals t, why do we assume there was no propellant that already got ejected (and therefore had its own momentum to contribute to the system momentum) prior to that time t?
It's all relative!
Shouldn't the velocity of the fuel be pointing downward??? And be Vr-U wrt the ground??
Yes it is. if this select upward as positive direction. In video 19.5 he selected upward + and then u=-u
I agree, and you are correct, he makes that change later in 19.5 video but it causes confusion for delaying that change until later videos
This was really usefull! Thanks a lot!
amazing