An object that is in simple harmonic motion is restored to its equilibrium position due to a force that is proportional to which quantity

To the displacement

Explanation:

In physics, an object is said to be in a simple harmonic motion if it oscillates under the action of a restoring force, which is given by

where

F is the force

k is a constant of the system

x is the displacement of the system, with respect to its equilibrium position

We see therefore from the equation that the force F is directly proportional to the displacement of the system, x. We also see that the direction of the force is opposite to that of the displacement (negative sign): so, the restoring force always tends to bring the system back to its equilibrium position.

An example of a simple harmonic motion is a mass oscillating on an horizontal spring. The restoring force acting on the mass is directly proportional to the elongation of the spring (displacement), and its direction is always towards the equilibrium position of the spring; as a result, the mass keeps oscillating back-and-forth around the equilibrium position under the action of the restoring force.

d.7.5cm is your answer