Nothing is accelerating ... it's not even moving. Everything is just sitting there.
That right there tells you that the forces are balanced wherever two things meet,
otherwise something would be accelerating.
At each level where two things meet, there are 2 forces:
-- The gravitational force ... the weight of everything above that place,
and
-- The upward force, exerted by everything below that place.
Here is the stack:
_____________
| Physics ... 2kg | weight = M G = 2 x 9.8 = 19.6 newtons
---------------------
|Calculus ..5 kg | weight = M G = 5 x 9.8 = 49 newtons
---------------------
|Econ . . . .3 Kg | weight = M G = 3 x 9.8 = 29.4 newtons
==================
-------- (Table) ----------
/ \
a). Surface where the table meets the Economics book.
Weight of everything above = (29.4 + 49 + 19.6) = 98 newtons
Upward force exerted on the Econ book by the table = 98 newtons.
b). Surface where the Econ book meets the Calculus book.
Weight of everything above = (49 + 19.6) = 68.6 newtons.
Upward force exerted on the Calc book by the Econ book = 68.6 newtons.
c). Surface where the Calculus book meets the Physics book.
Weight of everything above = 19.6 newtons.
Force exerted on the Physics book by the Calc book = 19.6 newtons.
