Two particles of equal mass $m$ have respective initial velocities $u \hat { i }$ and $u \left( \frac { \hat { i } + \hat { j } } { 2 } \right)$. They collide completely inelastically. The energy lost in the process is:\\
(1) $\frac { 1 } { 3 } m u ^ { 2 }$\\
(2) $\frac { 1 } { 8 } m u ^ { 2 }$\\
(3) $\frac { 3 } { 4 } m u ^ { 2 }$\\
(4) $\sqrt { \frac { 2 } { 3 } } m u ^ { 2 }$