A person standing on an open ground hears the sound of a jet aero plane, coming from north at an angle 60° with ground level. But he finds the aero plane right vertically above his position. If u is the speed of sound, speed of the plane is:
a. 

b. 
v 
c. 

d. 
v 
A person standing on an open ground hears the sound of a jet aero plane, coming from north at an angle 60° with ground level. But he finds the aero plane right vertically above his position. If u is the speed of sound, speed of the plane is:
a. 

b. 
v 
c. 

d. 
v 