Oscillator $y''+16y=\theta(\pi-t)$ with Heaviside forcing

Solve \(y ^ { \prime \prime } + 1 6 y = \theta ( \pi - t )\) with \(y ( 0 ) = y ^ { \prime } ( 0 ) = 0\) and where θ is the Heaviside function, \(\theta ( x ) = 0 { \mathrm { ~ i f ~ } } x < 0\) and \(\theta ( x ) = 1 { \mathrm { ~ i f ~ } } x > 0\)