When a wave collides with a boundary, what happens to the reflected wave?

When a wave collides with a boundary, the reflected wave has the same speed but opposite polarity. This is particularly true for waves reflecting off a fixed boundary, such as a solid wall. When the wave hits the boundary, it inverts because of the boundary's inability to provide any displacement; thus, the wave maintains its speed but alters its direction and phase. This inversion results in what is described as "opposite polarity" since the upward peaks of the wave become downward troughs upon reflection. In cases where the boundary is not fixed, the reflection may retain the same polarity, but the question specifies that it reflects in the context typical for waves reflecting off fixed boundaries. Understanding this concept is crucial in wave physics, particularly in analyzing wave behavior and properties in various mediums.