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513_Physics ProblemsTechnical Physics

# 513_Physics ProblemsTechnical Physics - Chapter 17 515...

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Chapter 17 515 between your sound impulse reaching each riser and the next. Whatever its material, each will reflect much of the sound that reaches it. The reflected wave sounds very different from the sharp pop you made. If there are twenty rows of seats, you hear from the bleachers a tone with twenty crests, each separated from the next in time by 2 0 6 340 0 004 . . m m s s a f b g = . This is the extra time for it to cross the width of one seat twice, once as an incident pulse and once again after its reflection. Thus, you hear a sound of definite pitch, with period about 0.004 s, frequency 1 0 003 5 300 . ~ s Hz wavelength λ = = = v f 340 300 1 2 10 0 m s s m m b g b g . ~ and duration 20 0 004 10 1 . ~ s s a f . P17.52 (a) λ = = = v f 343 1 480 0 232 1 m s s m . (b) β = = L N M M O Q P P 81 0 10 10 12 . log dB dB W m 2 I I v s s I v = = = × = = = × = × 10 10 10 1 26 10 1 2 2 2 1 26 10 1 20 343 4 1 480 8 41 10 12 8 10 3 90 4 2 2 2 4 2 1 2 8 W m W m W m W m kg m m s s m 2 2 2 2 3 e j e j e j b g e j . . max max . . . . ρ ω ρ ω π (c) ′ = = = λ v f 343 1 397 0 246 1 m s s m . λ λ λ = ′ − = 13 8 . mm P17.53 Since cos sin 2 2 1 θ θ + = , sin cos θ θ = ± 1 2 (each sign applying half the time)
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