SAT Subject Physics Practice Question 116: Answer and Explanation

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Question: 116

11. A bat emits a 40 kHz “chirp” with a wavelength of 8.75 mm toward a tree and receives an echo 0.4 s later. How far is the bat from the tree?

A. 35 m
B. 70 m
C. 105 m
D. 140 m
E. 175 m

Correct Answer: B


The speed of the chirp is

v = λf = (8.75 × 104−3 m)(40 × 103 Hz) = 350 m/s

If the distance from the bat to the tree is d, then the wave travels a total distance of d + d = 2d (round-trip distance). If T is the time for this round-trip, then

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