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Find how long a marble rolls down a ramp, given distance and angle

  1. Mar 9, 2014 #1
    1. The problem statement, all variables and given/known data
    How many seconds does it take a marble to run down a ramp with a length of 5.0 m and an angle of 6.9°?
    Correct answer = 2.9 s.

    2. Relevant equations
    v = at
    d = 1/2at2

    3. The attempt at a solution
    √2(5)/9.8≠2.9 s
     
  2. jcsd
  3. Mar 9, 2014 #2

    tiny-tim

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    hi camelCaseD! welcome to pf! :smile:

    where did you use the 6.9° ? :confused:

    (or the fact that it rolls)
     
  4. Mar 9, 2014 #3
    I'm not sure if the angle is relevant information for solving the problem or not. But the length of the ramp and the angle its at are the only given data I have. The marble does roll down the ramp.
     
  5. Mar 9, 2014 #4

    tiny-tim

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    ?? :confused: but if this 5m ramp was at 0.01°, wouldn't it take a lot longer than if it was at 90° ?
     
  6. Mar 9, 2014 #5
    Yes it would be slower if the angle were 0.01° than 90°.
     
  7. Mar 9, 2014 #6

    tiny-tim

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    yes! :smile:

    sooo … ? :wink:
     
  8. Mar 9, 2014 #7
    So then since the angle of the ramp is at 6.9° the time it would take the marble to roll down the ramp would take longer than if it were straight up and down.
     
  9. Mar 9, 2014 #8

    tiny-tim

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    yes, but what equation are you going to use?

    (and now i'm off to bed :zzz:)
     
  10. Mar 9, 2014 #9
    I'm going to use the equation d=1/2at2
     
  11. Mar 10, 2014 #10

    tiny-tim

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    (just got up :zzz:)
    yeeees …

    but first you need to find a (the component of acceleration down the ramp)!​

    what equation will you use for that? :smile:
     
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