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Homework Help: Projectiles physics problem - due tomorrow ;_;

  1. Nov 16, 2006 #1
    hey everybody, i would really appreciate a little help with this.

    I have a projectile, labeled zero, with mass m and velocity V. it travels in a parabolic motion until it reaches its apex, at which point it divides into two equal pieces, 1 and 2, with mass m/2 and m/2. Each of these pieces splits off with a velocity theta degrees from the horizontal.

    Now, i need to determine V1 initial and V2 initial in terms of V, theta, and unit vectors i^ and j^.

    Any help at all would really be appreciated - i have AIM(antigravityjesus) and MSN (antigravityjesus@hotmail.com).
  2. jcsd
  3. Nov 16, 2006 #2
    oh, forgot to say, this is the third part - i already found Delta K / K initial and solved some change-in-K relative to Theta equations.

    The problem is, if i sub kinetic energy = kinetic energy into conservation of momentum, i get V = V.

    Can i somehow use my Delta K/K equation here? im at a loss.

  4. Nov 16, 2006 #3
    okay, this is what ive done:

    1/2 m V^2 = 1/2 m 1/2 v1i ^ 2 + 1/2 m 1/2 v2i ^ 2
    which equates to
    V^2 = v1i^2 + v2i^2 / 4

    mV = mv1/2 + mv2/2
    which equates to
    V = (v1+v2)/2
    V^2 = (v1^2 + 2v1v2 + v2^2)/4
    ... which doesent directly equal v1i^2 + v2i^2 / 4 ... neat. let me see if i just accidentally solved something!

    The problem is, i dont have any equations with theta in it.
  5. Nov 16, 2006 #4
    nope, just gives me v1=0 and v2=0. darn.
  6. Nov 17, 2006 #5


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    Science Advisor
    Homework Helper

    Kinetic energy cannot be conserved in this process. It is first a conservation of momentum problem. If the angle θ is given, or your answers are supposed to be expressed in terms of θ then all you need is conservation of momentum.
    You can't find the change in kinetic energy without using momentum conservation to find the velocites, so I really don't get what you are saying here.
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