Question

A family ice show is held at an enclosed arena. The skaters perform to music with level 83.0 dB. This level is too loud for your baby, who yells at 78.0 dB (a) What total sound intensity engulfs you? W/m2 (b) What is the combined sound level? dB Need Help? Master It Talk to a Tutor 4 points SerPSE8 17.P035 A driver travels northbound on a highway at a speed of 24.0 m/s. A police car, traveling southbound at a speed of 35.0 m/s, approaches with its siren producing sound at a frequency of 2500 Hz. (a) What frequency does the driver observe as the police car approaches? Hz (b) What frequency does the driver detect after the police car passes him? (c) Repeat parts (a) and (b) for the case when the police car is traveling northbound while police car overtakes after police car passes Hz Hz

Answer 1

From beta = 10 log [I/10^-12 w/m^2] I = [10^beta/10] [10^-12 w/m^2] for your baby I_b = (10^78/10) (10^-12) = 6.30 times 10^-5 w/m^2 for the music I_m = [10^83/10] [10^-12] = 19.95 times 10^-5 w/m^2 The combined intensity is I_total = I_m + I_b = (19.95 times 10^-5) + (6.30 times 10^-5) w/m^2 = 26.25 times 10^-5 w/m^2 The combined sound level is B_total = 10 log [I_total/10^-12 w/m^2] = 10 log [2.625 times 10^-4/10^-12] = 84.19 dB \r\n The Doppler - shifted frequency if f' = f (V + V_0)/(V - V_s) f' = (2500) [343 + 24/343 - 35] = 2.978 KHZ = 2978 HZ After the police car passes f' = (2500 HZ) [343 + (-24)/343 - (-35)] = 2.109 KHZ = 2109 HZ while the police car overtakes f' = (2500) [343 + (- 24)/343 - 35] = 2589 HZ = 2.589 KHZ After the police car passes f' = (2500) [343 + 24/343 - (-35)] = 2427 HZ = 2.427 KHZ