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Unformatted text preview: Physics 21 Fall, 2011 Solution to HW-22 K20-7 The wave speed on a string under tension is 170 m/s. What is the speed if the tension is doubled? From Eq. (3) in the waves handout, v = p T /ρ, so if the tension T is doubled, v increases by √ 2. K20-11 A wave travels with speed 180 m/s. Its wave num- ber is 1.40 rad/m. What is its wavelength? What is its frequency? k = 2 π/λ ⇒ λ = 2 π/k = 2 π/ 1 . 40 = 4 . 49 m v = f λ ⇒ f = v/λ = 180 / 4 . 49 = 40 . 1 Hz K20-42 This is a snapshot graph at t = 0 of a 5.0 Hz wave traveling to the left. What are the speed and phase constant of the wave? D ( x, t ) = A sin( kx + ωt + φ ) . From the graph, λ = 2 . 0 m, and f = 5 . 0 Hz is given. Hence v = λf = 10 m / s . We already know the graph is at t = 0. At x = 0, the amplitude is abut 0.5. Since the maximum amplitude on the graph is 1, we have . 5 = 1 . 0 sin( k 0 + ω 0 + φ ) = sin φ ⇒ φ = 30 ◦ . K20-52 Earthquakes are essentially sound waves trav- eling through the earth. They are called seismic waves....
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This note was uploaded on 12/18/2011 for the course PHYS 021 taught by Professor Hickman during the Spring '08 term at Lehigh University .
- Spring '08