Sitting in newly launched gatiman express frequency of a stationary sound source is heard as `f` when it is approaching towards the source. What is the approximate speed of gatiman express if frequency heard when receding is `2f//3`? (take speed of sound in air as `320m//s`)

Options

A. `200km//h`
B. `190km//h`
C. `230km//h`
D. `250km//h`

Answer

C

Explanation

Assuming original frequency of signal as `f_(0)`
Frequency heard when approaching `f=(v+u)/(v)xxf_(0)`
When receding `(2f)/(3)=(v-u)/(3)xxf_(0)`
dividing them `implies(3)/(2)=(320+u)/(320-u)`
`impliesu=64m//s=64xx(18)/(5)km//hr`
`~=230km//hr`