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Q. A transverse sinusoidal wave is generated at one end of a long horizontal string by a bar that moves with an amplitude of $1.12\, cm$. The motion of the bar is continuous and is repeated regularly $120$ times per second. The string has linear density of $117\, g / m$. The other end of the string is attached to a mass $4.68\, kg$. The string passes over a smooth pulley and the mass attached to the other end of the string hangs freely under gravity.
The maximum magnitude of the transverse speed is :

Waves

Solution:

Tension in the string should be
image
$T=m g$
$T=46.8\, N$
Speed of wave should be
$v=\sqrt{\frac{t}{\mu}}=\sqrt{\frac{46.8}{0.117}}=20\, ms ^{-1}$
Power of wave on string is given as
$P=\frac{1}{2} A^{2} \omega^{2} \mu v$
$=\frac{1}{2} \times\left(1.12 \times 10^{-2}\right)^{2} \times(2 \pi \times 120)^{2} \times 0.117 \times 10^{-3} \times 20$
$=0.0834\, W$