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Homework Help: Please help projectile motion problem #2

  1. Sep 27, 2008 #1
    Please help!! projectile motion problem #2

    1. The problem statement, all variables and given/known data
    A girl throws a rock straight out form the roof of a building. the rock has a velocity of 25 m/s when it leaves the girl's hand, and the rock hits the ground 3 seconds later.
    1. how far from the bas e of the building does the rock land?
    2. how tall is the building?
    3. with what velocity does teh rock hit the ground?
    4. how far from the top of the builidng does the rock land?

    2. Relevant equations

    d=vit + (1/2)at2
    c2= a2 + b2
    tan theta= opp/adj

    3. The attempt at a solution

    I'm unsure if my answers are correct. however, I tried and this is what i got
    1. 75m
    2. 45m
    3. 39.05 m/s at 50.19o below ground
    4. 87.46m (this is the one I'm really unsure about)

    all help and inputs are greatly appreciated. thank you for your time and efforts.
  2. jcsd
  3. Sep 27, 2008 #2


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    Homework Helper

    Re: Please help!! projectile motion problem #2

    For 2, if you used 10 as acceleration of gravity then that would be correct. But the more correct answer would use gravity as 9.8m/s2

    I get a different answer for 3 by about 7 degrees but I think that may have to do with your treatment of part 2. I would guess your method is ok.
    Part 4 is good enough for Government work.

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