A swimming duck paddles the water with its feet once per time
interval of 1.7s , producing surface waves with this period. The duck
is moving at constant speed in a pond where the speed of surface
waves is 0.36 m/s , and the crests of the waves ahead of the duck have
a spacing of 0.19m .
1. What is the duck's speed?
Express your answer using two significant figures.
unit = m/s
2. How far apart are the crests behind the duck?
Express your answer using two significant figures.
unit = m
A swimming duck
2012-12-01 1:43 am
回答 (1)
2012-12-01 7:44 am
✔ 最佳答案
1. Frequency of wave produced by the duck = 1/1.7 Hz = 0.5882 HzFrequency of wave ahead of the duck = 0.36/0.19 Hz = 1.895 Hz
Using the Doppler Effect formula:
1.895 = 0.5882 x [0.36/(0.36-u)]
where u is the speed of the duck
solve for u gives u = 0.248 m/s
2. Use the Doppler Effect formula again.
frequency behind the duck = 0.5882 x [0.36/(0.36+0.248)] Hz = 0.3483 Hz
wavelength = 0.36/0.3483 m = 1.03 m
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