Final answer:
The correct answer is B) Closed; Mechanical energy is conserved within the system, as it is implied that no external forces act on the system, resulting in the conservation of mechanical energy.
Step-by-step explanation:
To determine whether the system containing only the object is open or closed with regards to mechanical energy, it is essential to understand the definitions of open and closed systems in the context of physics. An open system is one where energy can be transferred in and out, meaning mechanical energy might not be conserved if external influences such as work from external forces or heat transfer are present. Conversely, a closed system is isolated from its environment in such a way that no external forces work on it, and consequently, the mechanical energy within is conserved (KEi + PEi = KEf + PEf, where KE represents kinetic energy and PE represents potential energy).
Given these definitions, the correct answer is B) Closed; Mechanical energy is conserved within the system. This is because the statement in the question that excludes any external dissipative forces suggests that no mechanical energy is being transferred to or from the environment, hence making the system closed and conserving mechanical energy within it.