Question 11 0.77 pts Georgia is standing on the sidewalk waiting to cross the street on a day when the pressure and temperature in the air are sufficiently atypical that we must treat the speed of sound in air as an unknown. Two cars are driving by; a red Porsche and a Honda Accord. Perhaps not surprisingly, the Porsche is driving quite a bit faster than the Honda. When the Porsche is driving toward Georgia, the frequency of the sound it makes is 1.5% higher than when the Porsche is driving away from her. When the Honda i driving away from Georgia, the frequency of the sound it makes is 0.9% lower than when it's driving toward her. Show that if uc: is the speed of any car is at drives past Georgia, if v is the speed of sound in air, and if f and f are the frequencies she hears when the car is driving toward her and away from her respectively, then Use the equation you just derived to answer the following question: what percent higher is the speed of the Porsche compared to the speed of the Honda? 66 Question 12 0.77 pts. You're sitting at a bus stop, and a car is driving by. The car's speakers are playing a pure tone that its passengers perceive as having a frequency f. At the same time, a parked car nearby is playing a pure tone that you perceive has having the same frequency f. When the car is driving toward you, the tone from the car driving by combines with the tone from the parked car, and you hear a beat of frequency 4.58 Hz. When the car is dri ing away, you hear a beat of frequency 4.4 Flz. How fast is the car going in mph? There are about 1609 meters in a mile. Hint: If fieat;z is the observed beat frequency when the car is driving toward you, if fiest,4 is the observed beat frequency when the car is driving away from you, and if ug and v are the speed of the car and of sound in air respectively, then show that Fair _ 14 Fount, 1-% and then use this to solve for uc. 15 Question 13 0.77 pts Certain species of mice have a threshold of hearing below that of humans. Suppose you're sitting on a grassy knoll relaxing in the sunlight on a beautiful spring day out in the country. The air is still, and it's quiet. A bird is on the grass about two meters behind you and makes a faint rustling sound in the grass, and the sound is just barely at the threshold of your hearing. At the same time, the mouse whose hearing threshold is 3 dB is somewhere nearby, and the rustling sound is also at the threshold of its hearing. How far (in meters) is the mouse from the bird? (To check your answer, ask yourself if you expected the mouse to be further from or closer to the bird than you. Why?) 28