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

  • Thread starter blader324
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  • #1
blader324
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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?


Homework Equations





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?
 

Answers and Replies

  • #2
Doc Al
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How long does it take for the train to stop moving?
 
  • #3
blader324
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i think it takes 20 seconds...but I'm not so sure.
 
  • #4
Doc Al
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That's correct. If you're not sure, review the definition of acceleration.
 
  • #5
blader324
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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?
 
  • #6
Doc Al
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How did you deduce that? (Always show your work.)
 
  • #7
blader324
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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.
 
  • #8
Doc Al
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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.
 
  • #9
blader324
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thanks so much...i figured it out...and finally understand what I'm doing with all my other homework problems!
 

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