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Homework Help: Optics (Reflection of Light)

  1. Jul 29, 2014 #1
    A gun of mass 'M' fires a bullet of mass 'm' with a horizontal velocity 'v'. The gun is fitted with a plane mirror facing towards the receding bullet. Find the velocity relative to its image just after the gun is fired.
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  3. Jul 29, 2014 #2


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    The above is simply the problem statement. What are your thoughts on the problem? Where do you get stuck?
  4. Jul 29, 2014 #3
    Cannot proceed much....law of conservation of momentum needs to be applied i guess
  5. Jul 29, 2014 #4


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    So apply it and show what you get.
  6. Jul 29, 2014 #5
    I have solved but not sure if its correct. I have considered the velocity of the gun to be M. Now by conservation of linear mmntum, mv=MV.....therefore V = mv/M
    relative velocity wrt gun = v + V = mv/V + v = (m/M + 1)v
    Therefore relative vel wrt image = 2*v(m/M + 1) = 2v(m/M + 1) [ since image dist = objct dist for plane mirror ]
    Not sure....just check it.....thanks in advance :)
  7. Jul 29, 2014 #6


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    That's the general idea, but you would lose marks for lack of rigor (and multiple typos!).

    mv = -MV
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