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Average acceleration issue

  1. Jul 10, 2011 #1
    1. The problem statement, all variables and given/known data
    I will just try to post the whole questions, maybe my idiot eyes missed something...

    an arrow is accelerated for a displacement of 75cm [fwd]
    while it is on the bow, if the arrow leaves the bow at a velocity of 75m/s [fwd]
    what is it's average acceleration while it's on the bow


    2. Relevant equations
    t = displacement/ velocity
    a = velocity/time


    3. The attempt at a solution

    75 cm -> .75
    0.75 / 75 = 0.01s
    disp = 75m

    t = 75/0.75 = 100s
    velocity = 75m/s

    a = velocity / time
    time = displacement + velocity / velocity
    acceleration = velocity/(disp/velocity) = vecloity / 0.01 = 7500 WTH!?!?
     
  2. jcsd
  3. Jul 10, 2011 #2

    SteamKing

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    The arrow leaves the bow with a velocity of 75 m/s, but its initial velocity = 0 m/s
     
  4. Jul 10, 2011 #3
    ya it should be, according to logic I guess lol
    just i've been having a lot of trouble trying to figure out the average acceleration
     
  5. Jul 10, 2011 #4

    PhanthomJay

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    Average acceleration is the change in velocity divided by the change in time. You are not given the time. So you must assume a linear variation of acceleration while the arrow is in contact with the bowstring (it behaves like a spring), in which case you can use the standard kinematic equations to solve for the average acceleration.
     
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