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IIT JEE Advanced 2010 Paper 2
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© examsnet.com
Question : 8
Total: 57
Image of an object approaching a convex mirror of radius of curvature 20 m along its optical axis is observed to move from
25
3
m
to
4
50
7
m
in 30 s. What is the speed of the object in km per hour?
Your Answer:
Validate
Solution:
We have
1
f
=
1
v
+
1
u
For the first measurement,
v
1
= -25/3 m. Therefore,
u
1
=
f
v
1
v
1
−
f
=
10
×
(
25
∕
3
)
(
25
∕
3
)
−
10
= - 50 m
For the second measurement, we have
u
2
=
f
v
2
v
2
−
f
=
10
×
(
50
∕
7
)
(
50
∕
7
)
−
10
= - 25 m
Now, the speed is obtained as follows:
u
1
−
u
2
t
=
25
30
×
18
5
= 3 km/h
© examsnet.com
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