Momentum question. Acceleration on a moving track

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Discussion Overview

The discussion revolves around the concept of momentum and relative speeds in a scenario involving a moving train acting as a track for vehicles. Participants explore the implications of combining speeds when both the train and the vehicles are in motion, particularly focusing on the conditions under which these speeds might be considered additive.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant questions whether the speeds of a moving train and a vehicle on it can be combined, suggesting a scenario where both are moving at 100 mph.
  • Another participant challenges the notion of "instantly" accelerating to a higher speed when joining the train, prompting a clarification on the mechanics of acceleration.
  • Further clarification is provided that once on the train, a vehicle could indeed accelerate to a combined speed of 200 mph relative to the ground.
  • A hypothetical scenario is presented where a motorcycle on a moving train could achieve a speed of 200 mph relative to the ground, assuming both the train and motorcycle are moving in the same direction.

Areas of Agreement / Disagreement

Participants express some agreement on the mechanics of speed addition in the described scenario, but there remains uncertainty regarding the implications of instantaneous acceleration and the conditions under which speeds can be combined.

Contextual Notes

Participants do not fully resolve the assumptions regarding instantaneous acceleration and the specific conditions required for speed addition, leaving these points open for further exploration.

Berts
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Hi,

I've a question that is baffling me a little.

If a train was made so that it would act as a moving track / roadway and the cars were connected so as to complete a length of the track, in an oval for example. Say we accelerate the moving trackway to 100 Mph, and then a car accelerates to 100mph. Total speed = 200mph.

Now say you have a moving track on top of the railway track. Are all of the speeds combined, is it even possible? Would I imagine it would be like running on a travelator? So long as you joined the train at 100mph would you instantly accelerate to 200 mph?
It is hurting my brain and I know something in my thinking is incorrect!
 
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Berts said:
So long as you joined the train at 100mph would you instantly accelerate to 200 mph?
How did that "instantly" come into this?
 
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A.T. said:
How did that "instantly" come into this?
Ah yes I see now,

But once on the train you could then accelerate the vehicle and go 200mph...
 
Berts said:
Are all of the speeds combined, is it even possible?
I assume you mean something like this: Say a train is moving at 100 mph East with respect to the ground/track. And you, on the train, are riding a motorcycle at 100 mph East with respect to the train. (Pretend it's a long flat bed train.) Then your speed with respect to the ground will be 200 mph.

Is that what you mean?
 
Doc Al said:
I assume you mean something like this: Say a train is moving at 100 mph East with respect to the ground/track. And you, on the train, are riding a motorcycle at 100 mph East with respect to the train. (Pretend it's a long flat bed train.) Then your speed with respect to the ground will be 200 mph.

Is that what you mean?
Yes thanks :-)
 

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