(b) Acceleration, $a = - \omega^{2}y = \frac{- 4\pi^{2}}{T^{2}}y$ or $T = \left( \frac{4\pi^{2}y}{a} \right)^{1/2} = 2\pi\sqrt{\frac{y}{a}}$ $= 2 \times \frac{22}{7} \times \sqrt{\frac{3}{12}} = 3.14$
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Ph.D. in Physics with 19+ years of teaching experience.