A source moving through water at 10.0 m/s generates water waves with a frequency of 5.0 Hz. The speed of these water waves relative to the water surface is 20.0 m/s. The source approaches an observer who is at rest in the water. What wavelength would be measured for these waves by the stationary observer?
A)1.0 m
B)2.0 m
C)4.0 m
D)6.0 m
E)8.0 m

Question

Quizplus · Accepted Answer

The Doppler effect formula for waves in a medium is used here. The observed frequency is increased due to the source moving towards the observer. The observed frequency is f' = f(v + v_o)/(v - v_s), where v is the wave speed, v_o is the observer speed (0 m/s), and v_s is the source speed (10 m/s). The observed frequency f' = 5(20)/(20-10) = 10 Hz. The wavelength λ = v/f' = 20/10 = 2.0 m.

A Source Moving Through Water at 10