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Homework Help: 2-d momentum question

  1. Nov 10, 2007 #1
    1. The problem statement, all variables and given/known data

    A steel ball of mass 0.50 kg, moving with a velocity of 2.0 m/s [E], strikes a second ball of mass 0.30 kg, initially at rest.The collision is a glancing one, causing the moving ball to have a velocity of 1.5 m/s [E 30 N] after the collision. Determine the velocity of the second ball after the collision.


    2. Relevant equations

    Momentum = final momentum
    m1v1 +m2v2 = m1v1 +m2v2
    (c)^2 = (a)^2 + (b)^2 - 2(a)(b)cos C

    3. The attempt at a solution

    m1 = 0.50 kg
    v1 = 2.0 m/s[E]
    m2 = 0.30 kg
    v2 = 0 m/s
    v1 (final) = 1.5 m/s [E 30 N]
    v2 (final) = ?

    Ptotal = Ptotal (final)
    m1v1 + m2v2 = m1v1 + m2v2
    (0.50)(2.0[E]) = (0.50)(1.5[E 30 N]) + (0.30) (v2(final))
    1.0 [E] = 0.75[E 30 N] + 0.30(v2)

    Diagram i drew

    http://img259.imageshack.us/my.php?image=diagramhe8.png

    (c)^2 = (a)^2 + (b)^2 - 2(a)(b)cos C
    ((0.30)(V2))^2 = 0.75^2 + 1^2 -2(0.75)(1) cos 30
    0.09V2^2 = 2.5625 - 0.866025403
    V2 = square root(7.738606633)
    i used sign law to find out the equation
    V2(final) = 2.78[E 10.4 S]

    After doing all this work i went to the back of the book and the answer was 1.7 m/s[E 47 S] i hate when this happens:(
    if somebody can help me out i will really appreciate it

    thanks alot
     
  2. jcsd
  3. Nov 10, 2007 #2

    Astronuc

    User Avatar
    Staff Emeritus
    Science Advisor

    Separate it into N-S (y) and E-W (x) components. The net momentum in the y direction = 0, since initially there is no momentum in the y or transverse direction.

    Also consider conservation of energy.
     
  4. Nov 12, 2007 #3
    can somebody please show me how extacly i can solve this problem using components, i dont know where to start:frown:
     
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