Two masses m_A and m_B moving with velocities v_A and v_B in opposite directions collide elastically.  After that the masses m_A and m_B move with velocity v_B and v_A respectively.  The ratio $({\mathrm{m}}_{\mathrm{A}}/{\mathrm{m}}_{\mathrm{B}})$ is

• A

  1

• B

  $\frac{{\mathrm{v}}_{\mathrm{A}}-{\mathrm{v}}_{\mathrm{B}}}{{\mathrm{v}}_{\mathrm{A}}+{\mathrm{v}}_{\mathrm{B}}}$

• C

  $({\mathrm{m}}_{\mathrm{A}}+{\mathrm{m}}_{\mathrm{B}})/{\mathrm{m}}_{\mathrm{A}}$

• D

  ${\mathrm{v}}_{\mathrm{A}}/{\mathrm{v}}_{\mathrm{B}}$