Two soureces A and B are sending notes of frequency 680Hz.A listener moves from A to B with a constant velocity u. If the speed of sound in air is `360ms^-1`, what must be the value of u so that he hears 10 beats per second?

Options

A. `2.0 ms^-1`
B. `2.5 ms^-1`
C. `3.0 ms^-1`
D. `3.5 ms^-1`

Answer

B

Explanation

According to given condaitions ,
`V_1 =V_0[(V-V_0)/V]=[(V-u)/V]`
`V_2 =V_0[(V+V_0)/V]=[(V+u)/V]`
`V_2-V_1 =V_0[(V+u)/V]-V_0[(V-u)/V]`
`:. 10=V_0/V[V+u-V+u]
`10= `(2uV_0)/V`
`340xx10`=`2xx680u`
`:.u=2.5ms^-1`