Question

How to find relative speed of approach and relative speed of separation

Answer 1

I have not seen any formal definition, but this might work.

Let's assume that two bodies, left and right, move along x, with positive direction to the right.

Let's define the velocity of approach as positive and the velocity of separation as negative.

Then, the velocity of approach or separation could be determine as v⃗ =v⃗ left−v⃗ right.

For instance, if the bodies move toward each other, the velocity of the left body will be positive, the velocity of the right body will be negative, so the difference will be positive, showing that the bodies are approaching each other.

Another example, when the left body is moving to the left at 1m/s, while the right body is moving to the left at 3m/s. The difference will be −1−(−3)=+2, indicating the the bodies are approaching at 2m/s.