Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    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


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    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.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook