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Homework Help: Work,energy ratio

  1. May 29, 2016 #1
    1. The problem statement, all variables and given/known data

    4. Two bodies of mass m1 and m2 have equal momentum their kinetic energies E1 and E2 are in the ratio.

    ans. m2 : m1

    2. Relevant equations
    P= mv

    3. The attempt at a solution

    multiply both side by 2
    mv^2= m2v^2

    what should i do now? or the attemp is full wrong.
  2. jcsd
  3. May 30, 2016 #2
    Your attempt is wrong. How did you get E1 = E2?

    By the given question we have equal momentum [itex] m_1v_1 = m_2v_2 [/itex] We have to find out the ratio [itex] \frac{\frac{1}{2}m_1v^2_1}{\frac{1}{2}m_2v^2_2} [/itex] . Try to get the second ratio using the first equation.
  4. May 30, 2016 #3
    i dont know how to get the second ratio
  5. May 30, 2016 #4
    Well notice how you have to get [itex]v^2_1[/itex] and [itex]v^2_2[/itex] . So first off you square both sides and then try to remove the extra [itex] m_1 [/itex] and [itex]m_2[/itex]
  6. May 30, 2016 #5
    i got

    m1v^2=m2v^2 right?

    should i square both side now
  7. May 30, 2016 #6
    By squaring the equation you should get [itex] m^2_1v^2_1 = m^2_2v^2_2 [/itex]
  8. May 30, 2016 #7
    how can i get :-'
  9. May 30, 2016 #8
    give me the equation that i should try to solve
  10. May 30, 2016 #9
    Well using the equation [itex] m^2_1v^2_1 = m^2_2v^2_2 [/itex] you should get [itex] \frac{m_1v^2_1}{m_2v^2_2} = \frac{m_2}{m_1} [/itex]
  11. May 30, 2016 #10


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    Gold Member

    In your original attempt your very first equation was wrong. You wrote E1=E2. As Mastermind explained, that is not what you are given. You are given p1=p2, where pi=mivi. I see no evidence that you have understood that.
    Start again with the given information and show all your steps. Do not write "I got ...".
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