Question

A man generates a symmetrical pulse in a string by moving his hand up and down. At $t=0$ the point in his hand moves downward from mean position. The pulse travels with speed $3m/s$ on the string and his hand passes $6$ times in each second from the mean position. Then the point on the string at a distance $3m$ will reach its upper extreme first time at time $t=n/12$. Find $n$.

Answer 1

$t=0V=3m/sd=3m$

If hand passes $6$ times from the mean position in one second, than we know that string creates $3$ wavelength

$V=n\lambda 3=n\times 3n=1mt=\frac{1}{\lambda }\lambda =\frac{1}{n/12}=\frac{12}{1}=12$