Final answer:
The conversion of potential energy to kinetic energy in a spring system occurs when the spring is recoiling, as it releases the stored energy and the mass attached to the spring begins to move.
Step-by-step explanation:
The student has asked at what point in a sequence of events is potential energy being converted to kinetic energy. In the context of a spring system, this conversion takes place when the spring is released from a compressed or stretched position and begins to move back towards its equilibrium state. Specifically, the potential energy stored in the spring as elastic potential energy is converted to kinetic energy when the spring is neither fully compressed nor fully stretched but is in motion towards its equilibrium position.
When the spring is recoiling (option A), this is when the potential energy is converted into kinetic energy. The spring is in the process of releasing the stored energy, resulting in the mass attached to the spring moving. At the point where the spring is fully stretched (option B) or fully recoiled (option C), the energy is all potential energy. When the spring is stretching (option D), it is absorbing energy and converting kinetic energy into potential energy. Hence, the correct answer to the question is A, When the spring is recoiling.