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A fish rising vertically to the surface of water in a lake uniformly at the rate of 3 m/s observes a bird diving vertically towards the water at a rate of 9 m/s vertically above it. If the refractive index of water is (4/3), find the actual velocity of the dive of the bird. |
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Answer» Solution :If at any instant, the fish is at a depth x below the water SURFACE while the bird is at a height y above the surface, then the apparent height of the bird above the surface as seen - by fish will be `y_(ap) = mu_y` So the total apparent distance of the bird as seen by fish in water at depth x will be `h= x + MU y `(or) `(DH)/( dt) =(DX)/(dt) + mu ( dy )/(dt),i.e.,9= 3 + mu(dy )/( dt)` `i.e.,(dy)/(dt) = (6)/( (4//3)) = 4.5m//s` 
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