51

Suppose A and B in the previous problem change their positions in such a way that the line joining them becomes perpendicular to the direction of wind while maintaining the separation x. What will be the time lag B finds between seeing and hearing the drum beating by A ?

As seen in above diagram the resultant velocity of sound will be along AB and its magnitude AE can be calculated from the right angled triangle ACE.  

AE²=AC²-CE²  = v²-u²  

AE = √(v²-u²)   

So the time lag B finds between seeing and hearing the drum beating by A 

= Distance AB /velocity AE 

= x/√(v²-u²)