A particle starts executing simple harmonic motion (SHM) of amplitude $a$ and total energy $E$. At any instant, its kinetic energy is $\frac { 3 E } { 4 }$, then its displacement $y$ is given by:
(1) $y = a$
(2) $y = \frac { a } { \sqrt { 2 } }$
(3) $y = \frac { a \sqrt { 3 } } { 2 }$
(4) $y = \frac { a } { 2 }$