Question

A fish and bird are moving as shown in figure. Find the velocity of bird as observed by fish.

• A. $8m/s$ upwards
• B. $8m/s$ downwards
• C. $9m/s$ upwards
• D. $9m/s$ downwards

Answer 1

The correct option is A $8m/s$ upwards

Distance between bird and fish as observed by fish

$R=x+\mu y$

Differentiating w.r.t. 't'

$\frac{dR}{dt}=\frac{dx}{dt}+\mu \frac{dy}{dt}$

$\frac{dR}{dt}\to$ velocity of bird observed by fish

$\frac{dx}{dt}\to$ velocity of fish

$\frac{dy}{dt}\to$ velocity of bird

Taking downward direction as $+$ve

$\frac{dR}{dt}=-24+\frac{4}{3}\times 12$

$=-24+16$

$=-8$ m/s

i.e., $8$ m/s upward.