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Chapter_14_solved_problems_Physics_1301

Chapter_14_solved_problems_Physics_1301 - Chapter 14 solved...

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Chapter 14 solved problems 29. Picture the Problem: We need to calculate the wavelength of sound in air from its frequency. Strategy: Solve equation 14-1 for the wavelength, using 343 m/s for the speed of sound in air. Solution: 1. (a) Solve equation 14-1 for the wavelength: 343 m/s 0.807 m 425 Hz v f λ = = = 2. (b) Examine the relationship between wavelength and frequency: Wavelength is inversely related to frequency so, if the frequency increases the wavelength decreases. 3. (c) Calculate the wavelength at 450 Hz: 343 m/s 0.722 m 475 Hz λ = = Insight: As predicted, an increase in frequency corresponds to a decrease in wavelength. 48. Picture the Problem : The image shows a motorcyclist and police car approaching each other. Strategy: We want to calculate the frequency at which the motorcyclist hears the police car’s siren. In this problem both the source (police car) and the observer (motorcycle) are moving toward each other. Use equation 14-11, with the plus sign in the numerator and the minus sign in the denominator, to calculate the observed frequency. Solution: Insert the speeds and emitted frequency into equation 14-11: ( 29 ( 29 ( 29 o 1 1 1 13.0 m/s 343 m/s 512 Hz 577 Hz 1 27.0 m/s 343 m/s s u v f f u v + ′ = ÷ - + = = -

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