Question

Meaning of the underlined sentences

Answer 1

suppose there is a block
if a person push it from one side with a force of
10 newton in east direction and another man on the opposite direction with 5 newton force
the net force will be
10 newton - 5 newton
= 5newton in east
if both person push it from one side the net force is
10 newton + 5 newton
= 15 newton

Answer 2

1st sentence- it means that when we apply a force on an object in the direction it acts also as an opposite force.

2nd sentence- this sentence means that when when you apply two forces on same object from opposite directions that net force applied on it is the difference of the forces.