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**A stationary light source S wit ha natural frequency Fo is viewed in a mirror M by a stationary observer O. The mirror moves away from the observer wit ha velocty of Vrel << c**

**a) what frequency of light is recorded by a detector attached to the moving mirror**

because Vrel << c classical may be used

let F1 be this observed frequency observed

then [tex] f_{1} = f_{0} (1 - \frac{v_{rel}}{c}) [/tex]

is this correct??

**b) what frequency in terms of fo will the stationary observer measure for the light reflected off the mirror?**

the mirror will now emit the f1 from above wouldn't it ??

sine this mirror is moving away wouldnt the doppler shift be [tex] f_{2} = f_{1} \frac{c}{c+v_{rel}} [/tex]

which would be [tex] f_{2} = f_{0} (1 - \frac{v_{rel}}{c}) \frac{c}{c+v_{rel}} = f_{0} \frac{c-v}{c+v} [/tex]

but i got the second part wrong! Whats wrong with it??

**Also when asked for the lowest average speed of atom at some temperature T given some molar mass M**

which formula should be used??

is it [tex] v_{rms} = \sqrt{\frac{3RT}{M}} [/tex] or [tex]v_{avg} = \sqrt{\frac{8RT}{\pi M}} [/tex]

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