Explanation
Choose the correct option which describe the simple harmonic motion.
I. The acceleration is constant.
II. The restoring force is proportional to the displacement.
III. The frequency is independent of the amplitude.
The position of block executing SHM is $$x=A\sin\left(\dfrac{{2}{\pi}t}{T}+{\phi}\right)$$
where $$\phi$$ is the initial phase
given at $$t=0$$ , $$x=6cm$$ and $$A=6cm$$
therefore by above equation $$6=6\sin\left(0+{\phi}\right)$$
or $$1=\sin\phi$$
or $$\sin\dfrac{\pi}{2}=\sin\phi$$
or $$\phi=\dfrac{\pi}{2}$$
now time period of system $$T=2\pi\sqrt\frac{m}{k}$$
$$T=2\pi\sqrt\frac{4}{400}$$
$$T=\pi/5$$
so position of block $$x=6\sin\left(10t+\dfrac{\pi}{2}\right)$$
as the initial phase is in positive x-direction therefore $$+ $$ sign is taken there.
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