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Finding time to go up one floor

  1. Sep 12, 2015 #1
    • Member warned about posting without the template and with no effort
    Albert goes upstair on a moving floor. When he lets the moving floor make him go upstairs, it takes him 30 seconds. When he walks while being on the moving floor, it takes him 10 seconds. How much time would it take him to go upstair if the moving floor didn't work anymore (So, you can only walk)

    I have zero ideas what to do in this case. I think it might have something to do with relative speeds, but I'm not sure.
     
  2. jcsd
  3. Sep 12, 2015 #2

    Student100

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    You should really keep the template and make an attempt at the problem, even if you have no idea.

    Hint: What's the distance?
     
  4. Sep 12, 2015 #3
    By "moving floor" I assume you mean "escalator." What basic distance-velocity-time equation should you use?
     
  5. Sep 12, 2015 #4
    Sorry, next time I'll use it. Distance is speed times time.
     
  6. Sep 12, 2015 #5
    Yes, it's an escalator. I think I should use Distance = speed times time
     
  7. Sep 12, 2015 #6

    Student100

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    Don't worry about the equations, you're not to the point of using any equations yet.

    I'm asking whats the distance of the escalator. What is the problem trying to tell you physically.
     
  8. Sep 12, 2015 #7
    The problem doesn't provide any distance. In fact, the very next question is if I can guess the distance with the time only.
     
  9. Sep 12, 2015 #8

    Student100

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    Does it need to? Does the escalators length change? What can you tell me about the physical distance between the two points?
     
  10. Sep 12, 2015 #9
    Oh, the distance stays constant whatever the situation.
     
  11. Sep 12, 2015 #10

    Student100

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    Exactly. So if you picked an arbitrary value of 60 or 90 meters, would the answer change? Why don't you try that out.
     
  12. Sep 12, 2015 #11
    Well, depending on the distance, the time would vary. I mean, 10m is different from 1000m. But I think that the ratio of time would stay the same, regardless of the situation, right ?
     
  13. Sep 12, 2015 #12

    Student100

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    The times fixed in this case. So irrelevant of distance the time is the same. Did you try those two arbitrary distances?
     
  14. Sep 12, 2015 #13
    I got s= 1 m/s and 1/3 m/s for distance 10 m.
    s=10 m/s and 3,33333... m/s for distance 100m.

    Not sure if this is what you're asking for...
     
  15. Sep 12, 2015 #14

    Student100

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    If you had did 60 and 90 you'd get easier stuff to work with. :P

    Anyway, now what can we assume about the velocity? Is there an acceleration or is it constant? And what you can you say about the difference between just the escalator and the escalator and walking? Is it possible to determine walking speed and then find the time?
     
  16. Sep 12, 2015 #15

    Student100

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    You already have the answer, you just need to see it.
     
  17. Sep 12, 2015 #16
    Well, I get 2 m/s and 3 m/s for 30 seconds only. (This is the speed of the elevator, so the elevator is constant) I get 6 m/s and 9 m/s for 10 seconds. The difference is 6 - 2 = 4 m/s (This is the speed of walking of the person)
    9-3=6 m/s
     
  18. Sep 12, 2015 #17

    Student100

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    Okay, now how do you find the time from the 4m/s or 6m/s?
     
  19. Sep 12, 2015 #18
    Oh so the time is 15 seconds. So from my understanding, whether he walks at 4 m/s or 6 m/s, it takes him 15 seconds to climb the stairs of the non working elevator ?
     
  20. Sep 12, 2015 #19

    Student100

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    Yep, no matter the distance, the time is invariable that he takes to walk up the broken escalator. Some distances produce silly physical results (walking at incredible velocities), but that's the basis of this problem.

    Now you can answer the next problem relatively easily.
     
  21. Sep 12, 2015 #20
    So, the answer to the next problem would be no I can't guess the "Real" distance because there's no information indicating an exact distance for the elevator ? (We assumed distances to solve the problem)
     
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