Question

One train is approaching an observer at rest and another train is receding from him with the same velocity `4 m//s` . Both trains blow whistles of same frequency of `243 H_(Z)` . The beat frequency in `H_(Z)` as heard by observer is (speed of sound in air = `320 m//s`)
A. `10`
B. `6`
C. `4`
D. `1`

Answer 1

Correct Answer - B
`f_(b) = 243 ((320) / (320 - 4 ))- 243 ((320)/ (320 + 4)) = 6 H_(Z)`