A source of sound emitting a 1200 Hz note travels along a straight line at a speed of `170 m s^-1`. A detector is placed at a distance of 200 m from the line of motion of the source. (a) Find the frequency of sound received by the detector at the instant when the source gets closest to it. (b) Find the distance between the source and the detector at the instant it detects the frequency 1200 Hz. Velocity of sound in air` = 340 m s^-1`.

Answer

A, B, D

Explanation

Here, `V_s=170m/s`
`n_0=1200 Hz`
a. The frequency of sound received by detector (when source gets closest to it )
`=v/(v-v_scosv)xn_0`
`=340/(340-170xx(115.47/230.94))xx1200`
`=1600 Hz`
b. The detector will detect 1200 Hz frequency for energy emitted at minimum distance
`Then `=200/340=x/170`
`rarr x=100m

so, required distance
`=sqrt((200)^2+x^2)=sqrt((200)^2+(100)^2)`
`=224m`