Physics ch 15 number 13f

Question

The motion detector used in a physics lab sends and receives 30 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.

1) What is the wavelength of the waves emitted by the motion detector?

2) How long does it take for a pulse that reflects off an object 3.0m away to make a round trip?

Answer 1

first find the speed of sound in air at that temperature

v = 331.3 +(.606*C)

v = 331.3 +(.606*20) = 343.42m/s

v = fλ

343.42 = 30000λ

λ = .01145m

total distance is 6m

6/343.42 = .0175s