Final answer:
When work is done on an object by a non-conservative force, the object will either gain or lose mechanical energy.
Step-by-step explanation:
When work is done on an object by a non-conservative force, the object will either gain or lose mechanical energy. Non-conservative forces, such as friction, can convert mechanical energy into other forms of energy, such as thermal energy. So, option 3: Mechanical energy is the correct answer.