A boat is sent across the river with a velocity of 8 km/h. in a direction perpendicular to flow of river. If resultant velocity of boat is 10 km/h, then velocity of river flow is :

Options

A. 18 km/h
B. 2 km/h
C. 6 km/h
D. None of these

Answer

C

Explanation

Velocity of boat, `v_(b)`=8km/h

Let velocity of river flow =u
and resultant velocity of boat
w.r.t. river flow = `v_(r)`
`:.` From fig. `v_(r)^(2) =v_(b)^(2) + u^(2)`
`:. U=sqrt(v_(r)^(2) -v_(b)^(2))=sqrt(100-64)=6kmh^(-1)`