F = ma
Let the mass of the 3 carts be 3m.
F = (3m)a
a = F/(3m).....(1)
Now if the same force F is acted upon by a single cart, let the mass, be m.
F = ma
a = F/m........(2)
From equations (1) and (2) we can see the that the acceleration on the 3 carts is less than that on a single cart by (1/3).
That's if the each cart has the same mass.
