Question

which force best represents $f_{g}$?
a weight lifter is pushing a barbell upward with a force of 90 n.
the weight of a barbell acting on a weight lifter is 80 n.
the amount of upward force of a table on a box is 25 n.
a box on a rough table has difficulty sliding past 25 n of force.

Explanation:

$F_g$ represents the force of gravity. Gravity is a downward - acting force due to the weight of an object. The weight of a barbell acting on a weight lifter is a force due to gravity. The other options represent non - gravitational forces like applied forces (weight lifter pushing barbell upward) and normal forces (table on a box) or frictional forces (box on rough table).

Answer:

The weight of a barbell acting on a weight lifter is 80 N.