Two particles are projected simultaneously from two points \( \math...

Two particles are projected simultaneously from two points \( \mathrm{O} \) and \( \mathrm{O} \) ' such that \( 10 \mathrm{~m} \) is the horizontal and \( 5 \mathrm{~m} \) is the vertical distance between them as shown in the figure. They are projected at the same inclination \( 60^{\circ} \) to
\( \mathrm{P} \) the horizontal with the same velocity \( 10 \mathrm{~ms}^{-1} \). The time after which their separation becomes minimum is
(1) \( 2.5 \mathrm{sec} \)
(2) I sec
(3) \( 5 \mathrm{sec} \)
(4) \( 10 \mathrm{sec} \)