Phys101
Term:123
Online HW-Ch17-Lec02
Q1:
A child is swinging back and forth with a constant period and amplitude.
Somewhere in front of the child, a stationary horn is emitting a constant tone
of frequency f S . Four points are labeled in the drawing to indicate positions
along the arc as the child swings. At which position(s) will the child hear the
highest frequency of the sound from the whistle?
A.
B.
C.
D.
E.
at both A and D
at B when moving toward C
at C when moving toward B
at B when moving toward A
at C when moving toward D
Ans:
D
Q2:
A stationary source emits a sound wave of frequency 700 Hz. If it were possible for a
man to run towards the source at half the speed of sound, what frequency of emitted
sound he would hear? Answer in SI units and in 3 significant figures.
Ans:
f′ =
v + vD
v + 0.5 v
f=
f
v
v
f ′ = 1.5 f = 1.5 × 700 = 1.05 × 103 Hz
Q3:
A train approaches a mountain at a speed of 20.0 m/s. The train engineer
sounds a whistle that emits a frequency of 400 Hz. What will be the sound
frequency that the engineer hears reflected off the mountain? ( speed of
sound =340 m/s. Answer in Hz.
𝐀𝐧𝐬:
At the mountain f ′ =
v
340
f=
× 400 = 425 Hz
v − vs
340 − 20
Refelected Sound heard by the engineer:
f" =
v + vD ′
340 + 20
f =
× 425 = 450 Hz
v
340
KFUPM-Physics Department
1