An aero plane is going towards east at a speed of `510 kmh^-1` at a height of 2000 m. At a certain instant, the sound o the plane heard by a ground observer appears to come from a point vertically above him. Where is the plane at this instant? Speed of sound in air `=340 ms^-1`

Explanation

The sound reaching the ground observer P, was emitted by the plane when it was at the point Q vertically above his head. The time taken by the sound to reach the observer is
`t=(2000m)/(340ms^-1)=100/17s`
The distance moved by the plane during this period is
`d=(510kmh^-1)(100/17s)`
`=(30xx10^5)/3600m=833m.
Thus the plane will be 833 m ahead of the observer on its line of motion when he hears the sound coming vertically to him.