Two identical photocathodes receive light of frequencies $v_1$ and $v_2$. If the velocities of the photoelectrons (of mass $m$) coming out are $v_1$ and $v_2$ respectively,then:

• A
  $v_1 - v_2 = \left[ \frac{2h}{m}(v_1 - v_2) \right]^{\frac{1}{2}}$
• B
  $v_1^2 - v_2^2 = \frac{2h}{m}(v_1 - v_2)$
• C
  $v_1 + v_2 = \left[ \frac{2h}{m}(v_1 - v_2) \right]^{\frac{1}{2}}$
• D
  $v_1^2 + v_2^2 = \frac{2h}{m}(v_1 - v_2)$