An object of mass 0 . 5kg is executing simple harmonic motion. It...

$T = 2\pi\sqrt{\dfrac{m}{k}}$

$0 . 2 = 2\pi\sqrt{\dfrac{0 . 5}{k}}$

$k = 50{\pi}^{2}$

$\approx 500$

$x = Asin ( \omegat + ϕ )$

$= 5cmsin\left(\dfrac{\omegaT}{4} + 0\right)$

$= 5cmsin\left(\dfrac{\pi}{2}\right)$

$= 5cm$

$PE = \dfrac{1}{2}{kx}^{2}$

$= \dfrac{1}{2} ( 500 ) {\left(\dfrac{5}{100}\right)}^{2}$

$= 0 . 6255$