What is the formula for relative velocity?
GeneralClass 12AllAnswered 27 Mar 2026
Answer
Relative velocity of A with respect to B is:
v_AB = v_A - v_B
(vector subtraction). This tells you how fast and in what direction A appears to move from B's perspective.
Important cases:
- Same direction: subtract speeds (60 km/h - 40 km/h = 20 km/h)
- Opposite directions: add speeds (60 km/h - (-40 km/h) = 100 km/h)
- Perpendicular motion: use Pythagorean theorem √(v_A² + v_B²)
Example: If you're on a train moving 80 km/h and another train passes at 100 km/h in the same direction, its relative velocity is 20 km/h.
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