A fish rising up vertically toward the surface of water with speed `3ms^(-1)` observes a bird diving down vertically towards it with speed `9ms^(-1)` . The actual velocity of bird is

Options

A. `9.2m//s`
B. `4.5m//s`
C. `9.0m//s`
D. `3.2m//s`

Explanation

(b) Let any any time fish the depth of the`x` and `y` height at which bird was above the surface of water
`(d_(AC))/(d_(AP))=(mu_(1))/(mu_(2))impliesy/(d_(AP))=1/(mu)`
or `d_(AP)=muy`
`:.` Total appaent distance of the bird which was seen by a fish `x` distance in water.

`h=x+muy`
`(dh)/(dt)=(dx)/(dt)+mu(dy)/(dt)`
`9=3+mu(dy)/(dt)`
`(dy)/(dt)=6/((4/3))=4.5m//s`