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

K.E. of colliding body before collision =12mv2After collision its velocity becomesv'=(m1−m2)(m1+m2)v=m3mv=v3∴ K.E. after collision  12mv'2=12mv29Ratio of kinetic energy = K.E.beforeK.E.after=12mv212mv29=9:1