When some vehicle moves towards a stationary person, he finds difference in the frequency of horn by 2.5% of original frequency. If speed of sound is 320 m/s then, find speed of this vehicle.

Options

A. `8m//s`
B. `800 m//s`
C. `7m//s`
D. `80m//s`

Answer

A

Explanation

We have, `(f _(L))/( v + v _(L)) = (f _(S))/( v + v _(S))`
Here if `f _(S) = 100 Hz,` then `f _(L) = 102.5 Hz`
`therefore ( 102.5)/(320+0) = (100)/(320 -v _(S))`
`therefore 320 -v _(S) = (32000)/(102.5)`
`therefore 320 - (32000)/(102.5) =v _(S)`
`therefore v _(S) = ((320 xx 102.5) - 32000)/(102.5)`
`v _(S) = (800)/( 102.5) = 7.8 (m)/(s) ~~ 8 (m)/(s)`