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Homework Help: Find the Velocity of car A before the collision?

  1. May 22, 2005 #1
    Bumper cars A and B each have a mass of 100 kg. Bumper car A collides ealstically with bumper car B, which is at rest. After the Collision, the velocity of car A is 0.8 m/s 30degress north of east and car B is 0.6 m/s 60degrees south of east.

    1 Find the Velocity of car A before the collision?
    2. How would the problem change in the collision were inelastic?

    can sum1 please tell me where to even begin here, im completely lost.
  2. jcsd
  3. May 22, 2005 #2


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    Hi, theemassive1! Welcome to PF. Please note that there is a sub-forum especially for homework help. See https://www.physicsforums.com/forumdisplay.php?f=35 [Broken] . (But don'r repost there, the moderators will move your thread if they feel the need.)

    What you've got here is a conservation of momentum problem. The core equation is

    [tex]\sum_{k=A}^B \vec{p}_k^{initial} = \sum_{k=A}^B \vec{p}_k^{final}[/tex]

    where the [itex]\vec{p}_k^{initial}[/itex] are the momentum vectors of the bumber cars right before the collision, and the [itex]\vec{p}_k^{final}[/itex] are the momentum vectors of the bumber cars right after the collision. So after you've set up this equation and chosen a practical coordinate system (the standart is to take the y axis pointing south), the physics is over and all that remains to do is sort out the math: you know how to add vectors and you know that vectors are equal iff their components are equal. So solve for the unknowns: the x and y components of the velocity of A before collision.
    Last edited by a moderator: May 2, 2017
  4. May 22, 2005 #3
    ok, i got it now, thanks alot
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