A fork gives 5 beats with a 40 cm length of sonometre wire. If the length of the wire is shortened by 1 cm, the number of beats is still the same. The frequency of the fork is :

Options

A. 385 Hz
B. 600 Hz
C. 395 Hz
D. 400 Hz

Answer

C

Explanation

Here v = `(1)/(2l) sqrt(T//m)`
`therefore " " v l ` = constant
`therefore" " v_(1) l_(1) = v_(2) l_(2) `.
If v be the frequency of tunning fork.
`(v - 5) 40 = (v + 5) 39 `.
`rArr " " v = 395 ` Hz.
Hence the correct choice is (c).