A body is oscillating up and down at the end of a spring. Let's consider when the body is at the top of its up-and-down motion.
The displacement vector from the equilibrium position points up.

Question

A body is oscillating up and down at the end of a spring. Let's consider when the body is at the top of its up-and-down motion. 
The displacement vector from the equilibrium position points up.

Quizplus · Accepted Answer

When the body is at the top of its up-and-down motion, it has maximum displacement from the equilibrium position, which is downward. However, the displacement vector from the equilibrium position is always opposite in direction to the force acting on the body, which points upward (in this case, the force is the tension in the spring).

A Body Is Oscillating Up and Down at the End