Km can never be a negative number because Km denotes the concentration of an enzyme substrate at 1/2 Vmax of enzyme activity.

Can your distance be negative?

Distance cannot be negative, and never decreases. Distance is a scalar quantity, or a magnitude, whereas displacement is a vector quantity with both magnitude and direction. It can be negative, zero, or positive.

Is distance always positive?

The word distance means how far the object moves regardless of direction. It is always positive and is equal to the absolute value, or magnitude, of the displacement.