29. Light from an astronomical source is found to be shifted to a one pe rcent l

Question

29. Light from an astronomical source is found to be shifted to a one pe rcent lower frequency than had the source been at rest. What radial ve locity could cause such a shift?
A. 3.0×10^7 m/s moving away from the observer B. 3.0×10^6 m/s moving away from the observer C. 3.0×10^6 m/s moving toward the observer D. 1.5 ×10^6 m/s moving toward the observer E. 1.5×10^6 m/s moving away from the observer 29. Light from an astronomical source is found to be shifted to a one pe rcent lower frequency than had the source been at rest. What radial ve locity could cause such a shift?
A. 3.0×10^7 m/s moving away from the observer B. 3.0×10^6 m/s moving away from the observer C. 3.0×10^6 m/s moving toward the observer D. 1.5 ×10^6 m/s moving toward the observer E. 1.5×10^6 m/s moving away from the observer

Explanation / Answer

the relativistic doppler factor is

Fs/F0 = sqrt[(1-beta)/(1+beta)]

where beta = v/c

Fs= 99%*F0 =0.99*F0

(1-beta)/(1+beta) =0.9801

1- beta = 0.9801 +0.9801*beta

0.0199 =1.9801*beta

beta =0.010049997

V = c*beta

V = 3.015*10^6 m/s

The shift is toward lower frequencies (red shift), it means the source is moving away from the observer.

Correct answer is B)

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