Here's why:
* Relative Velocity: When considering the speed of an object relative to another, we're looking at how their positions change *compared to each other*.
* Same Velocity: If both buses have the same velocity, they are moving at the same speed *and* in the same direction. This means they are maintaining a constant distance between them.
* Zero Relative Speed: Since their distance isn't changing, the speed of one bus relative to the other is zero. Imagine you're sitting on one bus – you wouldn't see the other bus moving at all.
