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Homework Help: Collisions in 1 dimension

  1. Nov 27, 2004 #1
    On a frictionless horizontal air table, puck A (with mass 0.366 kg) is moving toward puck B (with mass 0.254 kg ), which is initially at rest. After the collision, puck A has velocity 0.119 m/s to the left, and puck B has velocity 0.655 m/s to the right.

    What was the speed of puck A (Vai) before the collision?

    K I put v=v1(m1+m2)/(m1-m2)

    v1=-.119 m/s since it moves in the left direction and i defined right as +ve

    my initial velocity of puck a came to be -0.659 m/s, but it seems to be wrong.

    Calculate , the change in the total kinetic energy of the system that occurs during the collision.

    for the KE I got 0.333 J but I don't know why its wrong
    thx guys
    Last edited: Nov 28, 2004
  2. jcsd
  3. Nov 28, 2004 #2

    Since puck B is initially at rest, the initial linear momentum of the system is: m1*v

    After the collision, the linear momentum will be equal to: m1*v1 + m2*v2

    Since linear momentum is conserved, the initial and final linear momentums will be equal. Once you equate these, you can solve for v.

    Hope this helps,

  4. Nov 28, 2004 #3
    yeah that helps thanks

    i was looking at it as an inelastic collision

    for the energy part i am using the equation

    1/2 m1 v1(squared)i = 1/2 m1 v(squared)1f + 1/2 m2 v(squared)2f

    question is looking for change in kinetic energy DURING collision

    i calculated Final KE - Initial KE but is that not considered the total change in KE DURING the collision?
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