How fast a car goes is known as its speed.
Speed = (distance covered) divided by (time to cover the distance)
It has nothing to do with the direction the car is going.
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The car's velocity is its speed AND the direction it's going.
30 miles per hour . . . speed
40 miles per hour north . . . velocity
20 miles per hour south
20 miles per hour west . . . . . same speed, different velocity
-- 'Velocity' is NOT a big word that you use when you mean
'speed' but you want to sound smarter. It's a different thing.
-- If you don't know anything about the direction the car is going,
then you can't say anything about its velocity.
-- If the car is going around a curve, then its velocity is constantly
changing, even if its speed is constant.