A car is moving along X-axis with a velocity `v=20m//s`. It sounds a whistle of frequency 660 Hz. If the speed of sound is `340m//s`. The apparent frequency heard by the observer `O` (shown in figure) is:

Options

A. `680Hz`
B. `640 Hz`
C. `700Hz`
D. `720Hz`

Answer

A

Explanation

`n=(v)/(v-v_Scos60^@)n`
Here `v=340 m//s, v_S=20 m//s, n=660Hz`
`n=(340)/(340-20(1)/(2))xx660=(340)/(330)xx660=680Hz`