Time period of oscillation is
$T=2 \pi \sqrt{\frac{M}{k}}$
When a another mass $M$ is also suspended with it as shown in figure $(b).$
Then,
Time period of oscillation is
$T^{\prime} =2 \pi \sqrt{\frac{M+M}{k}}=2 \pi \sqrt{\frac{2 M}{k}}$
$=\sqrt{2}(2 \pi \sqrt{\frac{M}{k}})=\sqrt{2} T \quad(\text { Using }(\mathrm{i}))$
$(A)\;y= sin\omega t-cos\omega t$
$(B)\;y=sin^3\omega t$
$(C)\;y=5cos\left( {\frac{{3\pi }}{4} - 3\omega t} \right)$
$(D)\;y=1+\omega t+{\omega ^2}{t^2}$