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Come to this Physics classroom (Page 2)

mellisai Viewbie
mellisai
mellisai

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Posted: 18 November 2008 at 1:00am | IP Logged
Thanks rajnish_hereakhl for the reply. I'm going to read it as soon as I come back from school! Thanks! 
-Grace- IF-Rockerz
-Grace-
-Grace-

Joined: 06 June 2008
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Posted: 03 February 2009 at 8:01pm | IP Logged
does anyone needs any formulas here?
if yes i've got some. i can post it if someone wants.
 
Im asking this b'cuz ppl are usually hesitant to ask simple questions.
 
Iqra
amrit23 IF-Dazzler

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Posted: 08 February 2009 at 8:31am | IP Logged
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akhl IF-Rockerz
akhl
akhl

Joined: 30 March 2007
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Posted: 08 February 2009 at 9:58am | IP Logged
Originally posted by amrit23

first of all..thnx alot for opening such a thread n that too on a subject like physics..

i was just wondering if u culd explain to me why is doppler's effect in sound asymmetric?

also..does anybody know any short cuts to the physics numericalsBlushing im just unable to solve them..


Once you understand fundamentals well, then solving numericals is easy. The following site is maintained by me. You can post questions there if you need any help.
http://www.visharadsoftware.com/forum

Dopper effect is asymmetric is because when the source is moving and the object is stationary, then the wavelength emitted by the source changes. As an analogy, suppose I throw one ball every at fixed time interval (say T). Since we are using this as an analogy of wave, let us ignore gravity or any other force. Suppose I have thrown 10 balls. If I am at rest, then distance between 1st and 2nd balls is the same as the distance between 2nd and 3rd balls and so on. But if I am moving and as earlier I throw balls at interval of T, then the balls will not be evenly spaced. This is same as saying that wavelength changes. But speed of sound relative to observer remains the same because the observer is at rest. Frequency = speed/wavelength. The speed is the same but the wavelength is different. This results in change in observed frequency.

But when source is at rest and observer is moving, then the source sees its waves evenly spaced. Thus wavelength emitted by the source remains the same. But speed of sound relative to observer changes. Frequency = speed/wavelength. The wavelength is the same but the speed is different. This results in change in observed frequency.

Thus in one case, Doppler effect is due to change in wavelength and in another case due to change in sound's speed relative to the observer. That is why the results are different.
-Grace- IF-Rockerz
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Joined: 06 June 2008
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Posted: 08 February 2009 at 5:15pm | IP Logged
Originally posted by amrit23

Originally posted by blushpink13

does anyone needs any formulas here?
if yes i've got some. i can post it if someone wants.
 


neki aur pooch poochLOL
plz post them..perhaps they might b the ones i needBig smile
ok, but i dont know cuz im in grade 9 i dont know abt you, but i'll post them anyways:)
angeleyesz Senior Member
angeleyesz
angeleyesz

Joined: 13 May 2008
Posts: 534

Posted: 09 February 2009 at 4:18pm | IP Logged
please help .. Embarrassed
im kinda lost on my assignment here in physics.. and was hoping i cud get some help from this classroom EmbarrassedEmbarrassed
 
1. what is the average speed of the bus that travels (8.2 +/- 0.2)km to the school in a time of (20 +/- 1)min?
 
2. Find the density of a cup of coffee that has a mass of (175.14 +/-  0.05)g and a volume of (180 +/- 5)mL.
 
3. What is the average speed of a sprinter when he runs (100.000 +/- 0.002)m in time of (9.12 +/- 0.01)s ? 
thanksyouu <3


Edited by angeleyesz - 09 February 2009 at 4:19pm
akhl IF-Rockerz
akhl
akhl

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Posted: 09 February 2009 at 10:45pm | IP Logged
1. what is the average speed of the bus that travels (8.2 +/- 0.2)km to the school in a time of (20 +/- 1)min?
 
Let
X = distance,
t = time,
v = average speed,
deltaX = uncertainty in distance,
deltat = uncertainty in time,
deltav = uncertainty in average speed
 
Without uncertainty:-
X = 8.2 km
t = 20 min
v = X/t = 8.2/20 = 0.41 km/min
 
Uncertainties:-
deltaX = 0.2 km
deltat = 1 min
deltav/v = deltaX/X + deltat/t
deltav/0.41 = 0.2/8.2 + 1/20
deltav/0.41 = 0.02 + 0.05
deltav/0.41 = 0.07
deltav = 0.07 * 0.41
deltav = 0.03 km/min
 
Therefore average speed = 0.41 +/- 0.03 km/min


Edited by akhl - 09 February 2009 at 11:07pm

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