What is the speed of a photon with respect to another photon if (a) the two photons are going in the same direction and (b) they are going in opposite directions?

Two photons having

What is the rest mass of photon?

When a photon stimulates the emission of another photon the two photon have

What is the momentum of a photon of frequency v ?

Point A and B are 90km apart from each other on a highway.A car starts from A and another from B at the same time.If they go in the same direction they meet in 9 hours and if they go in opposite directions they meet in 9/7 hours. Find their speeds.

Two trains take 3s to pass another when going in the opposite directions but only 2.5s if the speed of one is increased by 50% . The time one would take to pass the other when going in the same direction at their original speed is