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Simple kinematics question -- dropping a stone down a well

  1. Jul 6, 2015 #1
    1. The problem statement, all variables and given/known data

    A boy drops a 0.10 kg stone down a 150 m well and listens for the echo. If the speed of sound is 343 degrees Celsius, the how long after the stone is dropped will the boy hear the echo?

    2. Relevant equations

    v = d/t

    v2 = v2 + 2ax

    3. The attempt at a solution

    What I did was use v2 = v2 + 2ax to find the velocity of the rock at the end of the well. Then I used v = at to find how long it takes to go from zero to that final velocity. Therefore, I found that the time it took to get to the end of the well was 5.53 s. Next I used t = d / v to find how long it took the sound to travel back, which is .437 s. Thus, adding these together, I got 6 s, rounded to sig figs. Is this answer correct?
  2. jcsd
  3. Jul 6, 2015 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Looks good to me.
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