A car is moving towards a high cliff. The car driver sounds a horn of frequency f. The reflected sound heard by the driver has frequency 2f . If v is the velocity of sound , what will be the velocity of the car ?

Explanation

If ` u_(S) and u_(o) ` are the velocities of the source of sound and the listener respectively,
` frequency of the echo, ` f. = (v + u_(0))/( v - u_(s) )xx f `
Here, ` u_(s) = u_(0) ` = u (say) and f. =2f
` therefore 2f = (v + u)/(v-u) xx f " or " , v + u = 2 (v - u) ` or . 3u = v or , u = `v/3 ` .