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Physics - elastic problem

  1. Oct 10, 2010 #1
    1. The problem statement, all variables and given/known data

    Two balls of equal mass collide and stick together as shown in the figure. The initial velocity of ball B is twice that of ball A. (Take θ = 56°.)

    (a) Calculate the angle above the horizontal of the motion of mass A + B after the collision.

    (b) What is the ratio of the final velocity of the mass A + B to the initial velocity of ball A, vf/vA?

    (c) What is the ratio of the final energy of the system to the initial energy of the system, Ef/Ei?

    3. The attempt at a solution

    a) x= m ( 2vcos(56) + vcos(56) ) = 2mVfx

    2vcos(56) + vcos(56)= mvfx

    y = m ( 2vsin(56) + vsin(56) ) = 2mVfy

    2vsin(56) + vsin(56) = 2mVfy

    Am I suppose to take the magnitude of this ? How do I solve for two unknowns ?
    Do all the m's and v's cancel out?


    Attached Files:

  2. jcsd
  3. Oct 11, 2010 #2
    There is something bad in the setup of the first equation.

    Divide by the total mass of the body.
    v remains.
  4. Oct 11, 2010 #3
    2vcos(56) + vcos(56) = 2vfx => 3vcos(56)

    2vsin(56) + -vsin(56) = 2vfy => vsin(56)

    tan-1 ( y/x) => (1/3) => 26.3 degree
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