Mechanical energy is conserved in all the four situations
Explanation:
The law of conservation of energy states that in absence of non-conservative forces (such as air resistance of friction), the mechanical energy of an object is conserved.
The mechanical energy of an object is the sum of its potential energy (PE) and its kinetic energy (KE):
E = PE + KE = const.
In all the situations described, there are no air resistance or friction acting on the system, therefore mechanical energy is conserved in all the four situations described.
Learn more about kinetic and potential energy:
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-6.98 × 10-^7 is the answer <3
Modern theories reproduce caloric in the effective sense (similar to effective "particles" like phonons) for most phenomena it was used to explain. Mass was not really an issue because the fluid was assumed to be very "subtle" to easily permeate ordinary matter, and therefore to have negligible mass (from modern perspective, heating does add some minuscule mass due to mass-energy equivalence).
Plastic and wood is a couple