A body of mass $m$ moving with velocity $v$ collides head on with another body of mass  $2\, m$ which is initially at rest. The ratio of $K.E.$ of the colliding body before and  after collision will be 

  • A

    $1 : 1$

  • B

    $2 : 1$

  • C

    $4 : 1$

  • D

    $9 : 1$

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