Correct answer: m₁²/m₂²
The kinetic energy of a particle is given by E = (1/2)mv². For the two particles, the ratio of their kinetic energies is E₁/E₂ = (1/2)m₁v₁² / (1/2)m₂v₂² = (m₁v₁²) / (m₂v₂²). Using conservation of momentum, m₁v₁ = m₂v₂, so v₁/v₂ = m₂/m₁. Substituting this into the energy ratio gives E₁/E₂ = (m₁/m₂)².