In a fundamental mode,the time required for the sound wave to reach upto the closed end of a pipe filled with air is ' $t$ ' second. The frequency of vibration of air column is

A transverse wave is propagating on the string. The linear density of a vibrating string is $10^{-3} \mathrm{~kg} / \mathrm{m}$. The equation of the wave is $Y=0.05 \sin (x+15 t)$ where $x$ and $Y$ are measured in metre and time in second. The tension force in the string is