The kayak keeps its course perpendicular to the river bank at a speed, the module of which relative to the water υ1

The kayak keeps its course perpendicular to the river bank at a speed, the module of which relative to the water υ1 = 7.0 km / h. The module of the river flow velocity υ2 = 2.0 km / h. Find the module of speed υ of the kayak relative to the shore.

Since the speed vector of the kayak and the vector of the current speed are perpendicular, we will use the Pythagorean theorem to find the speed of the kayak relative to the shore.

V = √ (V1 ^ 2 + V2 ^ 2), where according to the condition V1 (own speed of the kayak) = 7 km / h, V2 (river speed) = 2 km / h.

Let’s do the calculation:

V = √ (7 ^ 2 + 2 ^ 2) = √ (49 + 4) = √53 = 7.28 km / h.

Answer: In relation to the shore, the module of the kayak’s speed is 7.28 km / h.