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Homework Help: Linear momentum with vectors

  1. May 29, 2006 #1
    Hello, I need help with my homework problem:

    A certain radioactive (parent) nucleus transforms to a different (daughter) nucleus by emitting an electron and a neutrino. The parent was at rest at the origin of an xy coordinate system. The electron moves away from the origin with linear momentum (-5.8 x 10-22 kg m/s)i; the neutrino moves away from the origin with linear momentum (-2.9 x 10-23 kg m/s)j. What are (a) the magnitude and (b) angle (from the +x axis) of the linear momentum of the daughter nucleus?

    I easily got part B, but I'm having a problem with part A. They want the momentum, so the equation to use is p=mv. However, I don't know how to get the velocity from the 2 vectors. It seems very easy and it probably is, but I'm not getting the answer right (I tried adding them, etc). I clearly see that i is x-direction and j is y-direction, but that's as far as I can get.

    I would appreciate it if someone can help. Thanks.
  2. jcsd
  3. May 29, 2006 #2


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    Why is that the equation to use? As you know, that relates momentum, mass, and velocity. What made you interested in velocity and mass?

    You should figure out what ideas you want to use to solve the problem, then figure out which equation to use.
    Last edited: May 29, 2006
  4. May 30, 2006 #3
    Thank you; you are right. Clearly I missed the word MAGNITUDE that was right in front of my face.
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