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Homework Help: Magnitude of the baseball's momentum?

  1. Mar 22, 2009 #1
    1. The problem statement, all variables and given/known data

    A cardinal (Richmondena cardinalis) of mass 3.80×10−2 kg and a baseball of mass 0.144 kg have the same kinetic energy. What is the ratio of the cardinal's magnitude of momentum to the magnitude of the baseball's momentum?

    p_c / p_b = ?

    attempt :

    P_c / p_b = M_c*V_c / M_b*V_b

    M_c / M_b = 19/72 ; their ratio

    so their V has to be a ratio of = V_c/V_b = 72/19.

    not sure what after this.
  2. jcsd
  3. Mar 22, 2009 #2


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    Homework Helper

    Re: Momentum

    {since they have the same kinetic energy)

    you can get mc/mb, so can get the ratio of the velocites.

    using the momentum equation you can get the ratios of the momentums

  4. Mar 22, 2009 #3
    Re: Momentum

    Confused a little.


    the .5 cancels out. I know M_c / M_b

    and I use

    SO Do i find the ratio of velocities and plug it into momentum ratio?
  5. Mar 23, 2009 #4
    Re: Momentum


    If I find the ratio of the velocity with [tex]\frac{0.5m_cv_c^2}{0.5m_bv_b^2}=1[/tex]
    then put the velocity ratio into :

    the ratio of momentum = 1.

    so i am not getting what your saying
  6. Mar 23, 2009 #5


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    Homework Helper

    Re: Momentum

    Ec = 1/2*mc*vc^2
    2*Ec*mc = (mc^2)*vc^2 = Pc^2.......(1)
    Similarly 2*Eb*mb = (mb^2)*vb^2 = Pb^2.......(2)
    Now take the ratio of equation 1 and 2 and find the ratio of the momentums.
  7. Mar 23, 2009 #6
    Re: Momentum

    [tex]K.E = \frac{p^2}{2m}[/tex]

    [tex]\frac{p_1^2}{p_2^2} = \frac{m_1}{m_2}


    [tex]\frac{p_1}{p_2} = \sqrt{\frac{m_1}{m_2}}

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