Is there a difference in speed between a car going forwards at 5m/s and a car moving backwards at 5m/s

There is NOT a difference in speed between a car going forwards at 5 m/s and a car moving backwards at 5 m/s.

Speed is just the rate of change of the position of an object. It is calculated by dividing the change in position (distance traveled) by the time it takes to move said distance.

The distance between the two points is always positive because the direction does not matter.

However, if we are looking for the velocity, the direction DOES matter. In this example, the velocity moving forwards is 5 m/s while the velocity moving backwards is -5 m/s.

In other words:

Speed is looking at the magnitude

Velocity is looking at the magnitude and direction.