Question

A boatman can row with a speed of 10km/h in still water. If the river flows at 5km/h, in which direction should boat man will row in water to reach a point on the other bank directly opposite to the point from where he started. The width of the river is 2km

Answer 1

Explanation:

angle = 90+30=120 degree with the direction of flow of water

Answer 2

Answer: The boatman should row by making an angle of 120° with the direction of the flow of the river.

Explanation:

Let OP represent the direction in which the river flows.

O is the starting point and R denotes the point where the boatman wants to reach.

Now, the vector OS represents the direction in which the boatman should row in order to reach the point R.

The vector OR shows the direction of the flow of the river.

OS = 10 kmph

SR = 5 kmph

sin θ = $\frac{SR}{OP} = \frac{5}{10} = \frac{1}{2}$ = sin 30°

or, θ = 30 °

or, ∠ROS = 30°

or, ∠SOR = ∠ROS + ∠ROP

= 30° + 90°

= 120°

Hence, the boatman should row by making an angle of 120° with the direction of the flow of the river.