question_answer

A man on the ground finds that when he sees a jet plane just over his head, the sound is heard at an angle of\[30{}^\circ \]with the vertical from his left. If the velocity of sound is v, what is the velocity of the jet plane?

A)  \[v/2\]                                

B)  \[2v\]

C)  \[v=\frac{2}{\sqrt{3}}\]                

D)  \[v\frac{\sqrt{3}}{2}\]

Correct Answer: A

Solution :

                 Let velocity of jet plane is v' \[\sin {{30}^{o}}=\frac{v'}{v}\] \[\Rightarrow \]               \[v'=v\sin {{30}^{o}}=v\times \frac{1}{2}=\frac{v}{2}\]