Particle A collides elastically (perfect) with another particle B which was at rest. They disperse in opposite directions with same speeds. Ratio of their masses respectively must be

From Law of conservation of linear momentumm1v1+0=−m1v+m2v⇒v=m1v1m2−m1...1Applying conservation of kinetic energy12m1v12+0=12m1v2+12m2v2 … (2)Solving (1) and (2) we get  m1:m2=1:3Therefore, the correct answer is (B).