Which is true according to the law of conservation of energy? A. In a closed system, the total amount of energy in the universe keeps on changing. B. The supply of energy is limited, so it is essential to conserve it. C. In a closed system, energy can be created and destroyed. D. In a closed system, energy cannot be used faster than it is created. E. In a closed system, the total energy always remains constant.

E. In a closed system, the total energy always remains constant.

Extra: The law of conservation of energy is a fundamental concept in physics, stating that energy can neither be created nor destroyed, only transformed from one form to another. This means that in any given isolated system (one that does not exchange any matter or energy with its surroundings), the total energy will remain constant over time. This principle applies no matter how energy is redistributed or changed among the objects within the system, including transformations between different types of energy, such as potential energy, kinetic energy, thermal energy, among others.

For example, when a ball is thrown into the air, its kinetic energy (due to its motion) is gradually converted into potential energy (due to its position in a gravitational field) as it rises. At the highest point, its kinetic energy is at a minimum, and its potential energy is at a maximum. As the ball falls back down, the potential energy decreases, and the kinetic energy increases. Throughout this entire process, no energy is lost. The total amount of kinetic and potential energy is conserved, assuming no air resistance or other external energy losses.

Energy conservation also has practical implications in everyday life and the environment. While the total energy in the universe remains constant, the quality or usefulness of that energy can change. For example, when fossil fuels are burned to produce energy in the form of electricity, the chemical energy is transformed into electrical energy which can perform work. However, some of that energy is also lost as heat, which is less useful for doing work. This is why energy conservation, as mentioned in option B, is essential—in the sense that we should strive to use energy as efficiently as possible and minimize energy waste.