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Asked by eknathmote50 | 08 May, 2019, 11:06: AM
Expert Answer
(A) Speed of image of fish as seen by bird directly
if y is the real depth of fish in water, apparent depth of fish as seen by bird = real depth/ refrative index = y/(4/3) = (3/4)y
speed of fish as seen by bird, if bird is at rest in air = (3/4)(dy/dt) = (3/4)×4 = 3 cm/s
Since bird is flying towards fish, speed of fish as seen by flying bird = (3+6) = 9 cm/s
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(B) Speed of image of fish formed after reflection from mirror as seen by bird
As given for case(A) fish is seen as moving with speed 3 cm/s towards bird at rest in air.
Then its image at miiror will move 3 cm/s away from bird at rest.
Since bird also moving in same direction as the image of bird moving, speed of image of bird as seen by flying bird = 6-3 = 3 cm/s
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(C) Speed of bird as seen by fish looking upward
If fish is at rest in water, then apparent distance of bird above water = refractive index × y = (4/3)×y
where y is real distance of bird above water.
Then speed of bird for fish at rest in water = (4/3)×(dy/dt) = (4/3)×6 = 8 cm/s
The speed of bird for a fish moving towards bird = 8 + 4 = 12 cm/s
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(D)Speed of image of bird as seen by fish looking downward
As given for case (C) speed of bird as seen by fish at rest in water = 8 cm/s.
Hence its image also move towards fish with 8 cm/s. But in this case fish also moving in the same direction as image is moving.
Hence speed of image of bird as seen by bird looking downward but rising upward = 8-4 = 4 cm/s
Answered by Thiyagarajan K | 08 May, 2019, 15:59: PM
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