Physics
Physics
Problem
The stream of a river is flowing with a speed of 2 km/h. A swimmer can swim at a speed of 4 km/h. What should be the direction of the swimmer with respect to the flow of the river to cross the river straight? a. b. c. d.Intuitive explanation
To cross a river straight (perpendicular to the banks), you need to think about vector addition: your swimming velocity and the river's current combine to give your actual path. The key insight is that you must aim upstream at an angle so that the river's sideways push exactly cancels your upstream component, leaving only a perpendicular crossing. Use the Pythagorean theorem or trigonometry to find the angle where your velocity vector and the current vector combine to point straight across.
Intuitive explanation
To cross a river straight (perpendicular to the banks), you need to think about vector addition: your swimming velocity and the river's current combine to give your actual path. The key insight is that you must aim upstream at an angle so that the river's sideways push exactly cancels your upstream component, leaving only a perpendicular crossing. Use the Pythagorean theorem or trigonometry to find the angle where your velocity vector and the current vector combine to point straight across.