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Homework Help: Help on free fall question

  1. Sep 14, 2008 #1
    1. The problem statement, all variables and given/known data

    an attacker at the base of a castle wall 3.65 m high throws a rock straight up with the speed 7.40 m/s at a height of 1.55 m above the ground. a.) will the rock reach the top of the wall? b.) if so, what is its speed at the top? if not, what initial speed must it have to reach the top? c.) find the change in speed of a rock thrown straight down from the top of the wall at an inital speed of 7.40 m/s and moving between the same two points. d.) does the change in speed of the downward-moving rock agree with the magnitude of the speed change of teh rock moving upward b/t the same elevations? explain physically why it does or does not agree

    2. Relevant equations

    xf=xi+ vxit+1/2axt2

    3. The attempt at a solution

    so for the first question, what i did was plug in the data for the above equation (making acceleration -9.80) and getting the time which is 9 seconds. so i took that as yes it does reach the top after 9 seconds, because i put xf as 3.65. so then i took the 9 seconds and plugged it in the equation and got 2.4 as the speed at the top. and then i dont know what to do for c.
  2. jcsd
  3. Sep 15, 2008 #2


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    Homework Helper

    Hi BeckyStar678,

    I don't believe this is correct; can you show how you got this result (what numbers you used and how you used them in the equation).
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