the Normal Force by the track is to keep the cart & load from sinking into the track.
it looks like the string is pulling somewhat upward but not entirely upward;
only the upward component will help the track not get sunk into.
Do you know that string's angle?
From a theory perspective: how much total mass is going to accelerate? (no, not 2.159kg)
which component of the string's Tension will be causing that acceleration?
Experimental perspective: did you measure its acceleration with the ticker tape?
then the horizontal component of string Force applied to (car & load) is pretty easy to deduce.
The theory, on the other hand, is a bear because the angle makes the hanger's acceleration different than the car & load acceleration.