Physics 21
Fall 2007
Solution to HW21
K 2011
A wave travels with speed 220 m/s. Its wave number is
1.50 rad/m. What is its (A) wavelength and (B) frequency?
(A) wavenumber
k
= 2
π
/
λ
, so
λ
= 2
π
/k
(B) Use
v = f
λ
.
v
was given, and
λ
was calculated in (A).
K 2013
The displacement of a wave traveling in the

y
direction
is
D
(
y,t
)=4.80cm sin(6.20
y
+ 61.0
t
), with
y
in m and
t
in s. What are
the (A) frequency (B) wavelength and (C) speed of this wave?
D
(
y,t
) = A sin(
ky
+
ϖ
t
),
k
=6.20 and
ϖ
=61.0 in SI units.
(A)
ϖ
= 2
π
f,
so
f
=
ϖ
/(2
π
) (B)
k
= 2
π
/
λ
so
λ
= 2
π
/
k
(C)
v
=
λ
f
= (2
π
/
k
)
ϖ
/(2
π
) =
ϖ
/
k
K 2042
This is a snapshot graph at
t
=0
of a 5.0 Hz wave traveling to the left.
What are (A) the wave speed and (B)
phase constant of the wave?
K 207
The wave speed on a string under tension is190 m/s.
What is the speed if the tension
T
is doubled?
From Eq. (3) in Waves Handout,
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 Spring '08
 Hickman
 Physics, Frequency, Wavelength, 0.3 m

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