The frequency of a radar is 780 MHz. When it is reflected from an approaching aeroplane the opponent frequency is more than the actual frequency by 2.6 kHz. The speed of the aeroplane is ……………. .

Options

A. 0.25 km/ s
B. 0.5 km/s
C. 1.0 km/s
D. 2.0 km/s

Answer

B

Explanation

`v. = (c + f)/(c - f) v implies v. - v = [(c + f)/(c - f) - 1] v " " [ v= c]`
`implies Delta v = (2vf)/(c - f) ~~ (2vf)/(c) implies v = (2 Delta v)/(2v) = (3 xx 10^(8) xx 2.6 xx 10^(3))/(2 xx 780 xx 10^(6)) = 0.5 xx 10^(3)` m/s