The state highway patrol radar guns use a frequency of 8.92 GHz. If you\'re appr

Question

The state highway patrol radar guns use a frequency of 8.92 GHz. If you're approaching a speed trap driving 41.3 m/s, what frequency shift will your FuzzFoiler 2000 radar detector see?

I got the answer: 1228 which is correct

I just cant get part B:
The radar gun measures the frequency of the radar pulse echoing off your car. By what percentage is the measured frequency different from the original frequency? (Enter a positive number for a frequency increase, negative for a decrease. Just enter a number, without a percent sign.)
Your car "sees" a shifted frequency because it is the observer. Once this wave bounces off your vehicle, the car becomes the source and the radar gun becomes the observer.

Explanation / Answer

From the Doppler's eqn we have
f = sqrt((c+u)/(c-u))*fo where c is the speed of light f0 is the gun frequency,f is the return frequency

So f = sqrt((3x10^8 + 41.3)/(3x10^8-41.3))*8.92x10^9Hz = 8920001227.97Hz

So the shift = 8920001227.97Hz - 8920000000Hz = 1227.97= 1228Hz

B) The % difference = 1228/8.92x10^9 * 100 = 1.38x10^-5

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