How long does it take for the train to stop moving?

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Homework Help Overview

The problem involves a train traveling at an initial speed of 20 m/s that begins to decelerate at a rate of -1.0 m/s² when the brakes are applied. The question focuses on determining how far the train travels during a 40-second interval after the brakes are engaged, considering that it will eventually come to a stop.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants express uncertainty about how to approach the problem, with one noting confusion over the application of formulas. Others suggest reviewing the definition of acceleration and question the reasoning behind deducing distances based on common sense rather than equations.

Discussion Status

The discussion includes various interpretations of the problem, with some participants suggesting potential answers and others questioning the reasoning behind those answers. There is a mix of attempts to clarify concepts and explore kinematic relationships without reaching a definitive consensus.

Contextual Notes

Participants mention the need to incorporate the fact that the train stops before the 40 seconds are up, indicating a potential misunderstanding of the relationship between time, distance, and acceleration in the context of the problem.

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Homework Statement


a train is traveling down a straight track at 20m/s when the engineer applies the brakes resulting in an acceleration of -1.0m/s^2 as long as the train is in motion. how far does the train move durin g a 40 second time interval starting at the instant the brakes are applied?


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The Attempt at a Solution


I'm new to physics and have no idea what to do. i keep getting zero when i plug it into the formula. also...i know that the train eventually stops before 40 seconds and doesn't travel anywhere...but how do i incorporate that into the equation?
 
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How long does it take for the train to stop moving?
 
i think it takes 20 seconds...but I'm not so sure.
 
That's correct. If you're not sure, review the definition of acceleration.
 
okay...so if it takes 20 seconds for the train to stop moving...doesn't that mean it travels for a total of 210 meters?
 
How did you deduce that? (Always show your work.)
 
i'm using common sense for the problem but i don't know what equation to use to get the answer of 200 meters. i just did 20+19+18+...+1+0=210 meters.
 
blader324 said:
i'm using common sense for the problem but i don't know what equation to use to get the answer of 200 meters. i just did 20+19+18+...+1+0=210 meters.
Commonsense is OK if you can justify it. What do those numbers mean? 20 = ?; 19 = ?...

If you are thinking that the train travels 20 m in the first second, etc., that's not quite correct. Hint: What's the average speed during the first second?

I suspect you should be learning some kinematic relationships.
 
thanks so much...i figured it out...and finally understand what I'm doing with all my other homework problems!
 

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