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 down wards from mean position. The pulse travels with speed 3 m/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 3 m with reach its upper extreme first time at t =

• A. $1.25$
• B. $1s$
• C. $\frac{13}{12}s$
• D. $\frac{23}{24}s$

Answer 1

The correct option is C $\frac{13}{12}s$

The time taken for the wave to reach $3m$ will be $t=\frac{3}{3}=1s$.

Since the wave begins from $x=0$ at $t=0$, we must add the time taken by the boy to move his hand form mean position to top position.

i.e. $\text{First one second to cover six mean positions}+\frac{\text{time taken to cover next mean position}}{2}$

$=1s+\frac{\frac{1}{6}}{2}s$

$=\frac{13}{12}s$