The formula that correctly relates the force and weight of the blocks is Fup = Fdown = mg.
Forces in equilibrium
The net force at a given equilibrium position is zero.
∑F = 0
According Newton's third law of motion, action and reaction are equal and opposite. That is, the force acting on an object is equal to the reaction exerted by the object.
Fa = -Fb
Thus, at the given equilibrium position, the force exerted by block Y on X is equal to the force exerted by block X on Y.
The formula that correctly relates the force and weight of the blocks is Fup = Fdown = mg.
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