Question

A string 120 cm long is fixed at one end. The other end is moved up and down with frequency 20 Hz. On a stationary wave 4 loops are formed. The speed of the progressive wave which moves along the string is ______.

Options

• 300 cm/s

• 600 cm/s

• 900 cm/s

• 1200 cm/s

Answer 1

A string 120 cm long is fixed at one end. The other end is moved up and down with frequency 20 Hz. On a stationary wave 4 loops are formed. The speed of the progressive wave which moves along the string is 1200 cm/s.

Explanation:

Given: n = 20 Hz

From the figure, 

2 λ = 120 cm

λ = 60 cm 

v = nλ

= 20 × 60 

= 1200 cm/s