Which equation represents the law of conservation of energy in a closed system?

KEi + PEi = KEf + PEf
PEi + PEf = KEi + KEf
KEi – KEf = PEi – PEf
KEi – PEf = PEi – KEf

Explanation:

A closed system is a system where exists energy interactions with surroundings, but not mass interactions. If we neglect any energy interactions from boundary work, heat, electricity, magnetism and nuclear phenomena and assume that process occurs at steady state and all effects from non-conservative forces can be neglected, then the equation of energy conservation is reduce to this form:

(1)

Where:

- Change in kinetic energy of the system, measured in joules.

- Change in gravitational potential energy of the system, measured in joules.

If we know that and , then we get the following equation:

(2)

Where and stands for initial and final states of each energy component.

Hence, the right answer is

answer: the rock sample is a sedimentary rock.

explanation:

it is given that:

mass of rock sample, m = 2.7 g

volume of rock sample,

so, density of rock sample will be

since, the density of rock sample is . hence, the rock sample is a sedimentary rock, whose densities varies between .