1just take the velocity of the source at the instant it leaves the signal and the velocity of the detector when it receives it in the frequency equation.
A source S and a detector D are initially at a distance of x=1km. Both start moving towards one another with same acceleration a = 10m/s2. Frequency of source is f = 2000Hz. Find the frequency observed by the detector at time t=4s. Speed of sound in air is v=300m/s
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1after t=4 seconds, source gives the signal, at that time velocity of source and observer both is 40m/s
Substituting these values in the equation I don't get the correct answer :(
answer is 2340.8 Hz
23its not a straight forward sum ,
btw frm where did u get this sum swordfish ? ekdam khatarnak sum hai
23suppose source emits a wave at time t1 wich is going to be received by observer at time t = 4
now for the wave emitted by the source
λt = λo - [(vsource at t ) To + 12aTo2 ]
= λo - (at To + 12aTo2 ) ...(1)
now for finding t
1000 - 12 ( 10 ) (42) - 12(10)t2 = v(4-t)
i.e distance that the wave emitted by source at time t needs to travel to reach observer at t=4 will be covered by the wave with vel v in time (4-t)
find t from here
now , this wave and observer meet at t=4 ,
now let T = time period of the wave as detected by observer
so at time 4-T , observer and this wave are at a distance λt wich is the wavelength of the wave .
and at time 4 sec , observer detects this wave .
so vT + v(observer at time 4-T) T + 1/2 aT2 = λt
so frm 1
vT + v(observer at time 4-T) T + 1/2 aT2 = λo - (at To + 12aTo2 )
frm this eqn find T , and the freq received by observer at t=4 will be 1/T
here To = 1/fo = 1/2000 , λo = vwave/fo
u will get t = 0.94832 sec
and freq received by observer = 2340.777 Hz
23solved it myself ,whom will i ask ????? but it took me half an hour just to frame the eqns !! btw i completed waves just a day ago, hence was able to solve :P, btw if u remember HCV me bhi ek accn ka sum hai on doppler , that sum helps a bit here
1I thought you might have asked your teachers.....
Yeah HCV last sum...I solved it....it helps very little...
How manny days did you take to complete theory + problems in waves?
23jo sir assignments dete hai , uske hi doubts hazaro hote hai , bahar ka sum puchega to he will ask who told u to do sums other than assignments and standard books and etc etc
theory i took may be 2.5 days ( frm resnick + sir notes ) , and solved HCV both chapters(very very easy sums ) in 1 day , and solved sir's asg( easy sums ) in 1 day
are that last sum of hcv solves half of dis sum ,
arey usme he told u to find freq at just t= 0 , but he also indireclty gav the idea to find freq at any t
but resnick has nicely given the explanation of doppler effect...
1solved HCV both chapters(very very easy sums ) in 1 day
solved sir's asg( easy sums ) in 1 day
By this do you mean that sums in HCV/asg. are easy for you or you solved only easy sums from them? [3]
71@Qwerty, Hope u clear IIT this year.
After that, I may take all of your assignment papers. You won't mind me giving me na? :) :) It might help me.
23are HCV sums are easy .. and si's asg on waves was relatively easy ( wich hapens only rarely )
thats bcz waves is such a chapter that u cant ask much difficult sums like thermo ...
for waves, if we kno the basics, then it is enuf for jee ( i hope )
btw tnx vivek [1]
btw those asg are mostly selected irodov sums and some concept clearing sums ..wich u might encounter in standard books ...in short ... a collection of good sums