A `400 m` wide river is flowing at a rate of `2.0 m s^-1`. A boat is sailing with a velocity of `10 m s^-1` with respect to the water, in a direction perpendicular to the river.
(a) Find the time taken by the boat to reach the opposite bank.

Answer

A, B, D

Explanation

Here the boat moves with the resultant velocity r, but the vertical component 10 m/s takes him to the opposite shore.
`tan theta = 2/10 = 1/5`
` Velocity = 10 m/s`
`Distance = 400 m`
`Time = 4008/10 = 40 sec`

b. The boat will reach the point C.
In `/_\ABC, tan theta = (BC)/(AB)= (BC)/400= 1/5`
`rarrBC= 400/5=80 m`