A wide, straight river flows due east with a uniform speed of relative to the ground.…
PHYSICS · Multi-part · AP · Physics 2: Algebra-based · Waves Sound and Physical Optics · Waves Sound and Physical Optics
Problem
A wide, straight river flows due east with a uniform speed of 5.0m⋅s−1 relative to the ground. A small boat equipped with a foghorn is initially allowed to drift with the current so that its speed relative to the water is zero. The horn emits a continuous tone of rest frequency 250Hz. A listener stands on the stationary north bank of the river.
(a) Determine the frequency heard by the listener while the boat is drifting with the current. Explain your reasoning.
(b) The boat’s engine is then engaged so that the boat travels due east at 5.0m⋅s−1 relative to the water. Calculate the new frequency detected by the listener.
(c) Compare your answers to parts (a) and (b), and discuss the roles played by the motion of the water and the boat in producing any difference between the two observed frequencies.