A loaded spring is set in simple harmonic motion. The force that tends to restore the load to its equilibrium position is

Analyze the question: We want the type of force that pulls a loaded spring's mass back toward its equilibrium position during simple harmonic motion (SHM).

Explain the concept: For SHM, the restoring force must be directly proportional to the displacement from equilibrium and directed opposite to it:

F = −kx

This is Hooke's Law. It describes the force a spring exerts when it is stretched or compressed. This force comes from the spring's ability to return to its original shape, which makes it an elastic force (also called the spring force).

Step-by-step solution:

1. When the load is pulled down, the spring stretches. The spring then pulls the load upward toward equilibrium.
2. When the load moves above equilibrium, the spring compresses (or is less stretched). It then pushes or pulls the load back downward.
3. In both cases, the force acts toward equilibrium and is proportional to the displacement. This is the elastic force of the spring.

Checking the other options:

• A. Adhesive: This is the attraction between unlike molecules (e.g., water sticking to glass). It has nothing to do with SHM of a spring.
• C. Frictional: Friction opposes motion and causes damping. It does not restore the load to equilibrium.
• D. Gravitational: Gravity acts constantly downward. It only shifts the equilibrium position (the spring stretches a little under the load). It is not the restoring force that causes the oscillation about that position.

Answer: B. elastic

Exam tip: Whenever you see "spring" and "restoring force" together, think Hooke's Law, F = −kx, elastic force. For a simple pendulum, by contrast, the restoring force is a component of gravity (weight).