ANSWER
• Gravitational potential energy: ,an object at rest
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• Kinetic energy: ,object moving horizontally
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• Both: ,object moving in either direction but changing its vertical position
Step-by-step explanation
Gravitational potential energy is the energy stored in an object due to its position, while kinetic energy is the energy that a moving object has due to its motion.
If the object is not moving, but we can consider that it will move - or was moved between different vertical positions, then we can use the gravitational potential energy equation to find the total mechanical energy the object has when it is at rest.
If the object is moving always at the same vertical position, then we can use the kinetic energy equation to determine the total mechanical energy the object has at that moment.
If the object is moving and also changing its vertical position - for example, if we throw a ball vertically it will have both kinetic and gravitational potential energy at different parts of motion, so we have to use both equations to determine the object's total mechanical energy.