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Homework Help: Elastic collision & Momentum

  1. Oct 27, 2008 #1
    A proton (mass 1 u) is shot toward an unknown target nucleus at a speed of 2.40×10^6 m/s. The proton rebounds with its speed reduced by 25% while the target nucleus acquires a speed of 3.50×10^5 m/s.

    What is the mass, in atomic mass units, of the target nucleus?




    I tried:
    Mp*Vip+Mn*Vin=Mp*Vfp+Mn*Vfn

    where Mp= Mass proton=1
    Vip= intial proton velocity=2.4E6
    Mn= Mass nucleus=unknown
    Vin=Initial Velocity of nucleus=0
    Vfp= Final velocity proton=.75(2.4E6)
    Vfn=final velocity nucleus= 3.5E5


    i get 1.71u but its wrong
     
  2. jcsd
  3. Oct 27, 2008 #2
    The final proton velocity has a minus sign
     
  4. Oct 27, 2008 #3
    Thank you very much got the answer
     
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