$\frac{1}{{2L}}\sqrt {\frac{T}{m}} = \frac{v}{{4L}}$…..$(i) $
and $\frac{1}{{2L}}\sqrt {\frac{{T + 8}}{m}} = \frac{{3v}}{{4L}}$ ..…$(ii)$
Dividing equation $(i)$ and $(ii),$ $\sqrt {\frac{T}{{T + 8}}} = \frac{1}{3} \Rightarrow T = 1N$
${y_1} = 2a\sin (\omega t - kx)$ and ${y_2} = 2a\sin (\omega t - kx - \theta )$
The amplitude of the medium particle will be