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
$T^{\prime} =2 \pi \sqrt{\frac{M+M}{k}}=2 \pi \sqrt{\frac{2 M}{k}}$
$=\sqrt{2}(2 \pi \sqrt{\frac{M}{k}})=\sqrt{2} T \quad(\text { Using }(\mathrm{i}))$

