What happens when a wave's wavelength is compressed by moving objects?

AI Thread Summary
The discussion focuses on the Doppler effect as it applies to a radar beam with a wavelength of 0.02 m and a frequency of 17,500 Hz, reflecting off a rocket moving towards a jet. The calculations initially presented were incorrect due to misapplication of velocities in the Doppler formula, which led to an incorrect echo frequency of 126,875 Hz. The rocket is determined to be blue shifted, indicating that the frequency increases as the source and observer move closer. It is emphasized that the speed of radio waves should be correctly identified, and the interaction of the wave with moving objects compresses the wavelength, resulting in a higher frequency. The discussion highlights the importance of accurately applying the Doppler effect equations to determine frequency shifts in both sound and light waves.
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Homework Statement


A radar beam has a wavelength of .02 m. The frequency is 17500 Hz. What would be its echo frequency if a rocket 60km away is moving at 500m/s and the radar is coming from a jet moving at 310m/s towards the rocket which is aimed at it? (b) Would the rocket appear red shifted or blue shifted? (c) Which would be shifted more, a sound wave or a light wave?

Homework Equations


[fo/vw + vo] = [fs/vw + vs]

The Attempt at a Solution



[fo/vw + vo] = [fs/vw + vs]
= [fo/ (350 + 310 + 500)] = [17500/ (350 + 310 - 500)]
fo = 126875Hz(b) Blue shifted

(c)Sound wave
Is this correct?
 
Last edited:
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No. The answer must be larger than 17 500 Hz.
Why do you have three velocities on each side when the formula only asks for two?
Both the 310 and the 500 must act to make the return frequency larger; make sure they have the correct signs to accomplish that.
It looks like you are using 350 m/s for the speed of radio waves - not correct!
 
What do you think would happen if a wave of a certain wavelength tries to fit into a smaller gap than the original separation of the moving objects??
 
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