Question

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

A. `6m//sec`
B. `4m//sec`
C. `3.5m//sec`
D. `4.5m//sec`

Answer 1

Correct Answer - D

Distance between bird and fish, as seen by fish
`s=x+muy`
`(ds)/(dt)=(dx)/(dt)+mu(dy)/(dt)`
`9=3+4/3*(dy)/(dt)`
`(dy)/(dt)=18/4=4.5m//sec`