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Homework Help: Rocket Momentum Problem

  1. Oct 25, 2013 #1
    1. The problem statement, all variables and given/known data

    A rocket explodes into two fragments with the following information:

    Initial trajectory: 150 m/s in the x-direction, mass is 40kg

    Portion a, post explosion: 45 degree angle above the horizontal, 25kg

    Portion b, post explosion: 30 degree angle below the horizontal, 15kg

    2. Relevant equations

    Conservation of momentum

    3. The attempt at a solution

    pi=150(m/s)*40kg=6000 kgm/s
    pa=Va[cos 45, sin 45]*25kg=Va(17.68+17.68[j])kg
    pb=Vb(cos 30, -sin 30[j])*15kg=Vb(12.99-7.5[j])kg

    By conservation of momentum: pi=pa+pb

    Two equations in two unknowns:


    Solving these gives me:

    Va=124.2 m/s
    Vb=292.8 m/s

    However this is wrong, the answer should be:

    Va=43.92 m/s
    Vb=146.41 m/s

    What am I doing wrong here? This is such a simple problem I am reviewing for the EIT, but I cannot for the life of me find out whats wrong and I am getting all the other momentum problems correct. Is the solutions manual incorrect?

    Thank you in advance for the help!
  2. jcsd
  3. Oct 25, 2013 #2
    Your solution looks good to me.
  4. Oct 25, 2013 #3

    rude man

    User Avatar
    Homework Helper
    Gold Member

    I agree, your sol'n is correct.
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