1oh shit...[57]hey thanks a lot yaar ....pata nahi kya soch rahi thi [1]
two trains A N B r moving with speeds 40 m/s n 60m/s resp in same direction in a straight line
track,with B ahead of A.THE ENGINES R AT front ends.the engine of train a blows a long whistle.assume that the sound of whistle is composed of components varying unifomly in frequency frm f1 to f2(f2>f1)with each component having same intensity.spread of frequency=highest frequency-lowest frequency.speed of sound in still air=340m
speed of sound ofwhistle
a)340m/s for passengers of A n 340m/s for passengers of B
b)300m/s for pass of A n 400m/s for passengers of B
c)380 m/s for pass of A n 280 m/s for passengers of B
D)300M/S for passe of A n 280 m/s for pasen of B
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24 Answers
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1it would be lower f1 to lower f2.
Using doppler's formulae, u'll find that both lower and higher frequency limits viz., f1 and f2 resp. decrease, as both the trains are moving in same direction. hence u must take it from lower f1 to lower f2.
1no actually if i m to decide bw lower f1 to lower f2 n higher f1 to higher f2 .which wud be crrct
1it means "from a value which is less than f1 to a value which is less than f2."
actually the term used in question is 'below' but i used 'lower'. hope that didn't confuse u.!
1i m sorry bt i understood nothing .cud u tell d meaning of lower f1 n upper f1
1for Q3, as the observer (passenger of train B) and the source (train A) are moving along same direction, there will be a decrease in frequency. hence intensity will be constant from lower f1 to lower f2.
also, the decrease in higher frequency will be more compared to decrease in lower frequency
(use doppler's formulae and u'll easily get it) hence the spread of frequency will be less. :)
1http://targetiit.com/iit_jee_forum/posts/iit_07_4392.html
i think it's a similar type of question....
so acc. to me ans is (c)....
1yaar since the speed of the sound to each passenger is same therefore the frequency heard by them is constant and also the intensity of each frequency in the spread is same....
ques 3...abhi soch rahan hoon
1q3distribution of intensity for passengers in train B
a)intensity is constant frm f1 to f2just as it is there at the sourcespread remaining the same
b)inten is constant frm above f1 to above f2,spread remaining the same
c)intensity is constant frm below f1 to below f2,spread becuming less
d)intensity is constant frm below f1 to bel f2,spread becuming more
1distribution of sound intensity of whistle as heard by passengers in train A
a)intensity is constant frm below f1 to below f2,spread remaining the same
b)intensity is constant frm f1 to f2as it is there at the source,spread remaining the same
c)intensity is constant frm below f1 to above f2,spread remaining same
d)intensity is constant frm above f1 to below f2,spread remaining same