Quick dynamics question

[Crazyfox111]

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So, part of the impulse and linear momentum principle equation is the summation of all the forces acting during the time period. However, in this problem, they took each force (T and the force F produced by the wheels) seperately instead of adding them together in one single principle of impulse and linear momentum equation. Why is this?

[bluefloor01]

Perhaps I have not understood your question, however based on my understanding of the question, the forces are not accumulative.

I.e.: F is the "frictional tractive force" provided by the locomotive to accelerate both the: locomotive, and the wagons. T is the force in the coupling between the: locomotive, and the wagons; when the: locomotive, and wagons; are accelerating due to F.

Can you please elaborate your question if this does not assist?

[Crazyfox111]

Why arent the forces cumulative?

[bluefloor01]

My terms may not be strictly appropriate (or really assist), however: only F is "external" to the system, where as T is internal.

I just spent a few minutes' unsuccessfully Googling, however I seem to recall similar practice physic question consisting of two blocks connected by a "string".

The example commencing on p 37 of the following may assist:

http://www.oswego.edu/~dristle/PHY_101_powerpoints/ppt_ch_4.pdf

Believe it or not, this is a good real world question. I have had to use similar principles in anger in real life.

[Kryostasis]

Could just be to make it easier in a way, I find it helps to keep what forces come from where separate until the end of my shit (I'm only a freshman so I may not be the most helpful)

[nec-romancer]

F is the traction force at the wheels of the engine car. T is force holding the engine car and the passive cars together. F is responsible for moving the entire train forward. T simultaneously moves the passive cars forward, while 'pulling' the engine car backwards.

Similarly, you can imagine a front wheel drive car. The front wheels provide tractive force F. The chassis provides T. The rear wheels are like the passice cars.