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KEAM 2020 Physics and Chemistry Solved Paper
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© examsnet.com
Question : 21
Total: 120
An object, moving in a straight line with velocity
100
ms
−
1
,
goes past a stationary observer. If the object emits note of
400
Hz
while moving, the change in the frequency noted by the observer as the object goes past him is (speed of sound in air
=
300
ms
−
1
)
350 Hz
300 Hz
200 Hz
100 Hz
150 Hz
Validate
Solution:
Given
f
=
400
H
2
;
c
=
300
m
∕
s
,
v
=
100
m
∕
c
Let
f
1
and
f
2
are the frequencies observed before and after train passes the observer.
Then,
f
1
=
f
C
C
−
v
=
400
×
300
200
=
600
H
2
f
2
=
f
C
c
+
v
=
400
×
300
400
=
300
H
2
∴
∆
f
=
f
1
−
f
2
=
300
H
z
© examsnet.com
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