A boat crosses a river with a velocity of `8(km)/(h)`. If the resulting velocity of boat is `10(km)/(h)` then the velocity of river water is

Options

A. `12.8 km//h`
B. `6 km//h`
C. `8km//h`
D. `10 km//h`

Answer

B

Explanation

`vec(v)_(r//g)=vec(v)hati,vec(v)_(b//r)=8 hatj, |vec(v)_(b//g)|=10`
`vec(v)_(b//g)=vec(v)_(b//r)+vec(v)_(r//g)=8hatj+vhati`
`|vec(v)_(b//g)|=sqrt((8)^(2)+v^(2))`
`10=64+v^(2) implies v=6km//h`