A bird in air is diving vertically over a tank with speed 6cm/sec. Base of tank is silvered. A fish…

Question

A bird in air is diving vertically over a tank with speed 6cm/sec. Base of tank is silvered. A fish in the tank is rising upward along the same line with 4cm/sec.

Column IColumn II(i) Speed of image of fish as seen by the bird directly[A] 12(ii) Speed of image of fish after reflection[B] 4(iii) Speed of image of bird relative to the fish looking upwards[C] 9(iv) Speed of image of bird relative to the    fish looking downwards in the mirror[D] 3

CGP EDU Academic Team · Accepted Answer

The correct answer is A. Step 1: Calculate the speed of the image of the fish as seen by the bird directly.  The speed of the bird diving downwards = 6 cm/sec. The speed of the fish rising upwards = 4 cm/sec. The speed of the image of the fish as seen by the bird is given by the sum of the speeds of both: Speed of image = speed of bird + speed of fish = 6 cm/sec + 4 cm/sec = 10 cm/sec. But we need to consider the speed of the bird diving down and that the fish is reflected in the mirror (the fish will seem to move down faster). Therefore, **total apparent speed** = Speed of bird + Speed of fish is viewed from a downward direction. Thus, The image speed = 6 + 6 (reflection) = 12 cm/sec.  Therefore, option [A] is correct.

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Column I	Column II
(i) Speed of image of fish as seen by the bird directly	[A] 12
(ii) Speed of image of fish after reflection	[B] 4
(iii) Speed of image of bird relative to the fish looking upwards	[C] 9
(iv) Speed of image of bird relative to the fish looking downwards in the mirror	[D] 3

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