Two people pull on a horizontal spring that is attached to an immovable wall. Then, they detach it from the wall and pull on opposite ends of the horizontal spring. They pull just as hard in each case. In which situation, if either, does the spring stretch more?

In first case

Explanation:

When two People pull the spring, let the applied force by each person be

and spring constant of spring be k

so Total force is

total extension according to Hooke's law is

When they detach the spring and apply force in opposite direction then force on either side is F so net extension is

so in first case there will be more extension