SOLUTIONS MANUAL
,Chapter 2 Solutions 1
Chapter 2 Solutions
2 1 2
2.1
z 2 2 t 2
2( z t )
z
2
2
z 2
2 ( z t )
t
2
2 2
t 2
It’s a twice differentiable function of ( z t ), where is in the negative z direction.
2 1 2
2.2 2 2
y 2
t
( y, t ) ( y 4t )2
2( y 4t )
y
2
2
y 2
8( y 4t )
t
2
32
t 2
Thus, 4, 2 16, and,
2 1 2
2
y 2 16 t 2
The velocity is 4 in the positive y direction.
2.3 Starting with:
A
( z, t )
( z t )2 1
2 1 2
z 2 2 t 2
(z t )
2 A
z [( z t )2 1]
2 2( z t )2 1
2 A 2
z [( z t ) 1] [( z t ) 1]
2 2 3 2
4( z t )2 ( z t )2 1
2 A 3
[( z t ) 1] [( z t ) 1]
2 3 2
3( z t )2 1
2A
[( z t )2 1]3
,2 Chapter 2 Solutions
(z t )
2 A
t [( z t )2 1]2
2 (z t )
2 A
t 2 t [( z t )2 1]2
4 ( z t )
2 A (z t )
[( z t ) 2
1]2
[( z t )2 1]3
[( z t )2 1] 4 ( z t )2
2 A
[( z t ) 1] [( z t )2 1]3
2 2
3( z t )2 1
2 A 2
[( z t )2 1]3
Thus since
2 1 2
z 2 2 t 2
The wave moves with velocity in the positive z direction.
2.4 c
c 3 10 8 m /s
5.831 1014 Hz
5.145 10 7 m
2.5 Starting with:
( y, t ) A exp[ a(by ct )2 ]
( y, t ) A exp[ a(by ct )2 ] A exp[ a(by ct )2 ]
2 Aa c c
2 y t exp[ a(by ct )2 ]
t b b b
2 4 Aa 2 c 2
2
c
4 y b t exp[ a(by ct ) ]
2
t 2 b b2
2 Aa c
2 y t exp[ a(by ct )2 ]
y b b
2 4 Aa 2
2
c
4 y b t exp[ a(by ct ) ]
2
y 2 b
Thus ( y, t ) A exp[ a(by ct )2 ] is a solution of the wave equation with c /b in the + y direction.
2.6 (0.003) (2.54 10 2 /580 10 9 ) number of waves 131, c ,
c / 3 10 8 /1010 , 3 cm. Waves extend 3.9 m.
2.7 c / 3 10 8 /5 1014 6 10 7 m 0.6 m.
3 10 8 /60 5 10 6 m 5 10 3 km.
2.8 5 10 7 6 10 8 300 m/s.
, Chapter 2 Solutions 3
2.9 The time between the crests is the period, so s; hence
1/ 2.0 Hz. As for the speed L /t 4.5 m/1.5 s 3.0 m/s. We
now know , , and and must determine . Thus,
/ 3.0 m/s/2.0 Hz 1.5 m.
2.10 = = 3.5 103 m/s = (4.3 m); = 0.81 kHz.
2.11 = = 1498 m/s = (440 HZ) ; = 3.40 m.
2.12 = (10 m)/2.0 s) = 5.0 m/s; = / = (5.0 m/s)/(0.50 m) = 10 Hz.
2.13 (/2 ) and so (2 /).
2.14
q /2 /4 0 /4 /2 3/4
sin q 1 2 /2 0 2 /2 1 2 /2
cos q 0 2 /2 1 2 /2 0 2 /2
sin(q /4) 2 /2 1 2 /2 0 2 /2 1
sin(q /2) 0 2 /2 1 2 /2 0 2 /2
sin(q 3 /4) 2 /2 0 2 /2 -1 2 /2 0
sin(q /2) 0 2 /2 1 2 /2 0 2 /2
q 5/4 3/2 7/4 2
sin q 0 2 /2 1 2 /2 0
cos q 1 2 /2 0 2 /2 1
sin(q /4) 2 /2 0 2 /2 1 2 /2
sin(q /2) 1 2 2 0 2 /2 1
sin(q 3 /4) 2 /2 1 2 /2 0 2 /2
sin(q /2) 1 2 /2 0 2 /2 1
sin q leads sin(q p/2).
2.15
x /2 / 4 0 /4 /2 3/4
2 x
kx /2 0 /2 3/2 2
cos(kx /4) 2 /2 2 /2 2 2 2 2 2 /2 2 /2 2 2
cos(kx 3 /4) 2 /2 2 /2 2 /2 2 /2 2 /2 2 /2 2 /2
2.16
t /2 /4 0 /4 /2 3 /4
t (2 / )t /2 0 /2 3/2
sin( t /4) 2 /2 2 /2 2 2 2 2 2 /2 2 /2 2 /2
sin( /4 t ) 2 /2 2 /2 2 /2 2 /2 2 /2 2 /2 2 /2