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Homework Help: Motion along a Straight Line problem

  1. Sep 21, 2005 #1
    Motion along a Straight Line problem !!!PLEASE HELP!!!

    An alert hiker sees a boulder fall from the top of a distant cliff and notes that it takes 1.30 s for the boulder to fall the last third of the way to the ground. You may ignore air resistance.

    I have calculated the last 1/3 of the distance to be 8.281 m by the formula y=(1/2)(a)(t^2) where a=gravity=9.8 meters per second.
    However to find the total distance of the cliff, I can't just multiply the distance of the last third times 3 because the boulder is accelerating throughout the entire distance, so how do I find the totatl distance?
    Last edited: Sep 21, 2005
  2. jcsd
  3. Sep 21, 2005 #2
    For some reaosn I'm stumped right now, but I can tell you that
    doesnt work because
    applies to this part of the problem too.
  4. Sep 21, 2005 #3


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    Homework Helper

    You only have distance moved and time to work with. And gravity of course.

    Let u be the velocity at beginning of last third
    Let v be the velocity when stricking the ground.

    Calculate u in terms of distance fallen
    Calculate v in terms of distance fallen

    The distance moved has been used. Can you now relate u and v in terms of t ?
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