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Escalator Question

  1. Sep 8, 2009 #1
    1. The problem statement, all variables and given/known data

    A shopper in a department store can walk up a stationary escalator in 30 s. The normally functioning "up" escalator can carry the standing shopper to the next floor in 42 s. Assume the same walking effort for the shopper whether the escalator is stalled or moving.

    How long will it take the shopper to walk up the moving escalator?

    How long will it take the shopper to walk down this upward moving escalator?

    If she escalator is stalled, the shopper will make the trip up and down the escalator:

    Faster
    Slower
    In the same time
    None of these

    2. Relevant equations

    I did not use any to solve the first part. I am unsure about the second part though.

    3. The attempt at a solution

    For the first question:

    1 / 30 + 1 / 42 = 2 / 35
    35 / 2 = 17.5 seconds

    I don't even really know where to start on the second part.

    I already wasted two attempts on this third part so the answer is either quicker or slower.

    This problem should be fairly easy to understand but for some reason I cannot wrap my head around the second and third parts.

    Any help is appreciated, thanks.
     
  2. jcsd
  3. Sep 8, 2009 #2

    rl.bhat

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    In the second part, the net velocity of the shopper is the difference of velocity of shopper and escalator.
     
  4. Sep 8, 2009 #3

    ideasrule

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    If you got the first part by doing this:

    1 / 30 + 1 / 42 = 2 / 35

    How come you couldn't get the second part by doing this?:

    1 / 30 - 1 / 42 = ...

    I really don't understand the third question. Faster or slower than what? Moving up the escalator? Going down the escalator?
     
  5. Sep 9, 2009 #4
    So that would mean that the net velocity of the shopper is 42 - 30 = 12. 42 is the velocity of the escalator and 30 is the velocity of the shopper. I do not know where to go from there. I do know that the answer has to be more than 30 because the shopper is walking downward with some upward related rate against her.

    I do not know if that would give me the correct answer for part two. I tried it and I came up with 1 / 105. If I take the inverse of that I get 105 which seems awfully high. I know the answer must be over thirty but 105 seconds to walk down an escalator that takes people up to the second floor slower than they can walk seems high. What do you think?

    For part three, the question is saying that if the escalator is stalled the shopper will make the trip up and down (combined) ... faster or slower.
     
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