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An object of mass m₁ collides with another object of mass m₂, which is at rest. After the collision the objects move with equal speeds in opposite direction. The ratio of the masses m₂:m₁ is

Asked in JEE Main 18th March 2nd Shift 2021 · Velocity exchange and mass ratios

• (1) 3 : 1
• (2) 1 : 2
• (3) 2 : 1
• (4) 1 : 1

Step-by-step solution

Why the other options are wrong

• (2) Comes from inverting the ratio and dropping the reversed momentum of m₁.
• (3) Comes from writing m₁u=m₂v with u=2v, forgetting that m₁ rebounds and carries momentum -m₁v.
• (4) Comes from equating equal speeds with equal masses; equal masses would leave m₁ at rest.

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