The motion detector used in a physics lab sends and receives 33 kHz ultrasonic p

Question

The motion detector used in a physics lab sends and receives 33 kHz ultrasonic pulses. A pulse goes out, reflects off the object being measured, and returns to the detector. The lab temperature is 20 degrees C.

Part A -
What is the wavelength of the waves emitted by the motion detector?
Express your answer using two significant figures.
= ________mm

Part B -
How long does it take for a pulse that reflects off an object 3.0 m away to make a round trip?
Express your answer using two significant figures.
t = _________ms

Explanation / Answer

Given frequency of pulse f = 33 KHz speed of sound   v = 343 m/s    a)    wave length of wave emitted by the motion detector                                     = v / f                       = 343 / 33*103 Hz                      = 1.03939 cm                         = 10.3939 mm b) time taken for a pulse  that reflects off an object 3.0 m away to make a round trip                   t = 2 d / v                       = 2 ( 3 ) / 343                       = 0.0174 s

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