In the following situations a light is being directed towardsyou by the object d

Question

In the following situations a light is being directed towardsyou by the object described. In which of the following will you(the observer) see a LOWER frequency (a redshift)than what the source is emitting? Choose all that apply.
1. A police car iscircling you. You are stationary. 2. A fire truck ismoving towards you while traveling 50 mph.You are moving towards it while traveling 40 mph.
3.An ambulance is stationary.You are moving away from it while traveling 50 mph.
4. A train is moving awayfrom you while traveling 50 mph. You arestationary. 5. Aflying saucer is stationary. You are moving away from it whiletraveling 50 ft/min. In the following situations a light is being directed towardsyou by the object described. In which of the following will you(the observer) see a LOWER frequency (a redshift)than what the source is emitting? Choose all that apply.
1. A police car iscircling you. You are stationary. 2. A fire truck ismoving towards you while traveling 50 mph.You are moving towards it while traveling 40 mph.
3.An ambulance is stationary.You are moving away from it while traveling 50 mph.
4. A train is moving awayfrom you while traveling 50 mph. You arestationary. 5. Aflying saucer is stationary. You are moving away from it whiletraveling 50 ft/min.

Explanation / Answer

(3) In this case velocity of the source is vs = 0 Velocity of the observer is vo = 50mph                                         = 22.352m/s Then the apparent frequency heard by the observer is                       f' = [(v - vo)/v]f                          = 0.932f             [since v = 331m/s] (4) WHen the source (train) is moving away from the stationary observerthen the apparent freq heard by the observer is                f' = (v / (v+vs))f                  = 0.934 f (5) If the observer is moving away from the stationary source then theapparent frequency heard by the observer is            f ' =[(v - vo)/v]f Here vo = 50ft/min = (50)(0.3048m) / (60s)    = 0.254m/s Then f ' = 0.999f So correct options are (3) and (4)

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