Revise GCSE Physics

Question:How is relative velocity calculated?

By simply doing a vector subtraction of the two velocities.

First a sign convention must be chosen; such as RIP or right is positive.

Then one values must be subtracted from the other it does not matter which way round, as long as you remember the signs the sign gives the direction relative to the 1st car in you subtraction.


CAR 1= 40m/s to the right; CAR 2= 50m/s to the left.

CAR 1 = +40 m/s ; CAR 2 = -50 m/s

40 (-50) = +90 m/s


-50 (+40) = -90 m/s

The signs indicate the direction of the relative velocity towards the car you started from.