You may be talking about a different question. There were at least 2 different tests given, so although that was the only doppler shift on mine and Seen's test, there may have been a different one on urs. In fact thats probly the case. In the question Im talking about a source is moving towards a wall and they ask about the frequency heard back at the source.
The_Seer wrote:For the doppler effect problem,
The problem gives a car moving at 1/10 the speed of sound emitting frequency f_0 to a stationary wall, and asks what the car observes when it listens to the reflection of the emitted frequency. In this case, the frequency is equal to f_0 (1+v)/(1-v), which is f_0 / 0.82. It wasn't a typo.
YF17A wrote:I think it's actually (8000/40000)^2 for the apogee-perigee question...since area is 1/2 R^2 theta, and theta is approximately v delta t, equal areas in equal times means (v_2/v_1) = (R_1/R_2)^2.
michael879 wrote:The_Seer wrote:For the doppler effect problem,
The problem gives a car moving at 1/10 the speed of sound emitting frequency f_0 to a stationary wall, and asks what the car observes when it listens to the reflection of the emitted frequency. In this case, the frequency is equal to f_0 (1+v)/(1-v), which is f_0 / 0.82. It wasn't a typo.
ok first, I was trying not to repeat the exact question since we DID all sign a nondisclosure agreement. Second, where did you get that formula? I applied the doppler shift equation twice and got f = f_0/.81. The other options were f_0/.9, f_0 * .9 and f_0 * .81 (forget the 5th). .81,.9,1/.9,1/.82? Seems like a typo to me.. If not on the right answer than on one of the wrong answers.
michael879 wrote:The_Seer wrote:For the doppler effect problem,
The problem gives a car moving at 1/10 the speed of sound emitting frequency f_0 to a stationary wall, and asks what the car observes when it listens to the reflection of the emitted frequency. In this case, the frequency is equal to f_0 (1+v)/(1-v), which is f_0 / 0.82. It wasn't a typo.
ok first, I was trying not to repeat the exact question since we DID all sign a nondisclosure agreement. Second, where did you get that formula? I applied the doppler shift equation twice and got f = f_0/.81. The other options were f_0/.9, f_0 * .9 and f_0 * .81 (forget the 5th). .81,.9,1/.9,1/.82? Seems like a typo to me.. If not on the right answer than on one of the wrong answers.
The_Seer wrote:michael,
Take a look at this site http://galileo.phys.virginia.edu/classes/152.mf1i.spring02/DopplerEffect.htm to see why the above formula holds. Basically, for the source moving its f(1+v), and for the observer moving it's f/(1-v), so in this case, where the source and the observer is moving, we get the combined result.
G01 wrote:The answer is f_0/.82 right?
michael879 wrote:G01 wrote:The answer is f_0/.82 right?
yep, we got the right answer for the wrong reason .
Maxwells_Demon wrote:Yeah, I went over that equation the night before, so I got it.
Thinking about the test in my dreams, etc., I figured I got 2 wrong so far. ugh... But it's hard for me to recall any questions to think about them in particular because I flew so fast taking the test....
Maxwell's Demon
The_Seer wrote:YF17A wrote:I think it's actually (8000/40000)^2 for the apogee-perigee question...since area is 1/2 R^2 theta, and theta is approximately v delta t, equal areas in equal times means (v_2/v_1) = (R_1/R_2)^2.
YF17A, theta would be equal to (v delta t) / R radians, not just v delta t, hence making the ratio (8000/40000), not (8000/40000)^2.
Take a look at this site if you need detailed explanation.
http://www.physicsforums.com/showthread.php?t=83333
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