Question

The frequency of a radar is $780MHz$. The frequency of reflected wave from aeroplane is increased by $2.6kHz$. Velocity of the aeroplane is :

• A. 0.25 km/s
• B. 0.5 km/s
• C. 1.0 km/s
• D. 2 km/s

Answer 1

Answer: (B)

The velocity of aero plane $v=\frac{1}{2}\frac{\Delta nc}{n}$
Given, $\Delta n=2.6kHz=2.6\times 10^{3}Hz$,
$c=3\times 10^{8}m/s$,
$n=780MHz=780\times 10^{6}Hz$
$v=\frac{1}{2}\frac{2.6\times 10^3\times 3\times 10^8}{780\times 10^6}$
$v=0.5\times 10^{3}m/s$
$v=0.5km/s$