Let's imagine a spring is attached to a rigid wall.One end is free to move. Now I exert force on that end and make some elongation there. According to Newton's 3rd law, there should be a action reaction pair. So a restoring force will be occured in the spring. But when I loose that end there shouldn't be any restoring force(because I no longer exert any force) in the spring and the spring should remain in such an elongated state. But reality differs . Why?
Second question is that, if restoring force and external force are action reaction pair then they are equal in magnitude. which means that we cannot exert a constant force I mean external force can't be constant because restoring force being -kx depends on x which is a variable. But common sense says it's easily possible to exert constant force.
However I am literally stuck in these two conceptual questions and will be glad to see detailed answer.