GENERAL KNOWLEDGE

Detailed explanation-1: -The initial mechanical energy of a system equals the final mechanical energy for a system where no work is done by non-conservative forces (conservation of mechanical energy principle).

Detailed explanation-2: -Initial kinetic energy is the amount of kinetic energy initially, when you first start paying attention (or at the start conditions of your problem). Final kinetic energy is the amount of kinetic energy at the point when you stop paying attention, or reach the final conditions of your problem.

Detailed explanation-3: -Remember the law of conservation of energy: the total energy at the beginning equals the total energy at the end. In this case, we have only potential energy at the beginning and only kinetic energy at the end. (The initial velocity is zero, and the final height is zero).

Detailed explanation-4: -The total energy E of a system is simply the sum of its internal, kinetic, an potential energies: E=me=m(u+ke+pe)=U+KE+PE.