Relative Motion in Two Dimension: Practice Problem & Solution

Solution Explained:

To solve this problem, we apply the core principles of Relative Motion in Two Dimension. Understanding the underlying formula is key to arriving at the correct answer below:

For minimum crossing time, the swimmer must head perpendicular to the river bank. The net ground velocity is the vector sum of swimmer's velocity and river velocity: \(v_g = \sqrt{v_{\text{sw}}^2 + v_r^2} = \sqrt{8^2 + 4^2} = \sqrt{80} \approx 8.94\text{ m/s} \approx 9\text{ m/s}\).