1. The problem statement, all variables and given/known data A spring with spring constant 50 N/m is pulled with 10 N force at both ends of the spring. So, the extension of spring length is.. A. 0.0 m B. 0.1 m C. 0.2 m D. 0.3 m E. 0.4 m 2. Relevant equations F = k Δx 3. The attempt at a solution F = 10 N <--- 0000000000000000000000 ----> F = 10 N I think the Δx should be 20/50 = 0.4 m But, the teacher said that it should be 0.2 m. He said that it's like a common problem where the spring is attached to the wall, and we pull it. The wall exerts the reaction force which magnitude is the same as the pulling force, but in opposite direction (reaction force). But, then I think, if the reaction force given by the wall is the same magnitude as the action, the spring won't get stretched, right? I think the reaction force must be less than the one I exert on the spring.. Which one is correct?? Please help me... I somehow don't get the insight.