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

Um, how does this make sense?

  1. Sep 19, 2004 #1
    Hey guys, im a new member here and i dont know that much about physics so if this seems really obvious to you sorry, im only 15!

    Ohk heres my problem.
    I was looking at some stuff on impact
    Now impact is reliant on impulse yes?
    Now if I(impluse) = F average * change in time
    And impulse is = momentum
    momentum is Mass * Acceleration, or delta v / delta t
    So if a bird is travelling at a velocity of 10m/s with a mass of 10kg but has no acceleration and it collides with an aeroplane which is travelling at 80m/s with a mass of 12 tons with no acceleration does that mean there is no impact as there is no acceleration?
  2. jcsd
  3. Sep 19, 2004 #2


    User Avatar
    Science Advisor
    Homework Helper

    When they collide each object undergoes acceleration - the bird moreso than the airplane! :-)
  4. Sep 19, 2004 #3
    Oh i see, it all makes sense now thnx
  5. Sep 19, 2004 #4
    oh im an idiot i see now, p = mv, not ma, ma is f... oh well i feel dumb now, should probably get my formulae right first
  6. Sep 20, 2004 #5

    Doc Al

    User Avatar

    Staff: Mentor

    incorrect signs

    Not exactly. The net change in momentum is zero, so:
    [tex]m_1(V'_1-V_1)= -m_2(V'_2-V_2)[/tex]
    Again, your signs are incorrect. If the collision is elastic (certainly not the case for the bird hitting the plane!) then KE is conserved, so:
    [tex]m_1V'_1^2 + m_2V'_2^2 = m_1V_1^2 + m_2V_2^2[/tex]
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook