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Conservation of linear momentum problem

  1. Sep 24, 2013 #1
    1. The problem statement, all variables and given/known data
    A particle of mass 5m moving with speed v explodes and spilts into two pieces with masses of 2m and 3m. The lighter piece continues to move in the original direction with speed 5v relative to the heavier piece. what is the actual speed of the lighter piece?



    2. Relevant equations
    using law of conservation of linear momentum
    initial moment = final moment
    mass (m) x Velocity (v) = mass (m) x Velocity (v)


    3. The attempt at a solution

    using the formula...

    5m (v) = 2m(v) - 3m (5v) ....) i used the minus (-) sign because the heavier piece went a different direction

    5mv = 2mv -15mv

    20mv = 2mv

    10v = v

    but my answer was wrong....

    PLEASE HELP EXPLAIN WHY AND WHAT IS IT IM MISSING TO DO>>>

    FIRST CLASS TEST IS TOMORROW!
     
  2. jcsd
  3. Sep 24, 2013 #2

    CWatters

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    That's not correct. You appear to be assuming that after the explosion the large bit is moving five times faster than the small bit. That's not what the problem states.

    I wouldn't recommend that. I would just define

    Vi is the initial velocity
    Vsmall as the new velocity of the small bit
    Vlarge as the new velocity of the large bit

    So with that in mind it should be something like

    5mVi = 2mVsmall + 3mVlarge

    I'll let you figure out the other equation to write.

    Sorry for the edits to my reply.
     
  4. Sep 24, 2013 #3
    ok soo would i know say

    5mVi - 3mVlarge = 2mVsmall

    Ok i think im confusing myself but i do get and understand what you were saying....i think the "relative" word in the problem is what confusing me...

    what do they mean when they say ".....with a speed 5v relative..."
     
  5. Sep 24, 2013 #4
    Pleas Helppp...i really want to understand this
     
  6. Sep 24, 2013 #5
    Im still stuck on this question can someone give any insights..? PLEASE...
     
  7. Sep 25, 2013 #6

    haruspex

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    2016 Award

    Yes
    it's how much faster it's moving. Vsmall = Vlarge + 5v.
     
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