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# Conservation of Energy Questions

In an isolated system, total energy always remains constant; this is known as the law of conservation of energy. In other words, energy can be neither created nor destroyed, and it can only transform into different forms. In particle collisions (classical mechanics), the sum of the kinetic energy of the particles before the collision is equivalent to the sum of the kinetic energy of the particles after the collision. The kinetic energy, depleted by an object slowing down as it moves upward against the gravitational force, is considered as being transformed into stored energy or potential energy. Later, it is transformed back to kinetic energy as the object speeds up in the course of its return to the ground.

In the case of a simple pendulum, it swings upward and downwards. When the pendulum holds still briefly at the peak of its swing, the kinetic energy is practically zero, and the system’s entire energy components will be completely related to potential energy. When the pendulum knob comes back down, the potential energy is transformed back to kinetic energy. Every time the sum of the kinetic and potential energy is constant. However, friction slows down most physical mechanisms, especially motion (dissipating the energy constantly).

The video is about the essential concepts of kinetic energy and mechanical energy.

The ideal conserved quantity is the sum of thermal, potential and kinetic energy. For example, when a box slips down a ramp, the potential energy becomes kinetic energy. When friction restricts the box’s motion to a stop, the kinetic energy is transformed into thermal energy. Just like the conservation law states, no new energy is created or annihilated. It only changes the form (it changes from potential energy to kinetic energy to thermal energy). The first law of thermodynamics is another version of the energy conservation law.

The energy conception has expanded to incorporate the energy of an electric current, the energy accumulated in a magnetic or an electric field. For instance, a bus starts to move when the fuel’s chemical is transformed into kinetic energy (motion). In classical physics, conservation of energy was different from conservation of mass. This conception drastically changed with the introduction of the special theory of relativity. It states that mass is directly related to energy by the equation

$$\begin{array}{l}E = mc^2\end{array}$$
. This proves that the mass-energy as a whole is conserved. In other words, this shows that any system with mass can itself be transformed into complete energy and vice versa (only activates under extreme conditions).

## Important Conservation of Energy Questions with Answers

1) What is meant by conservation of energy?

In an isolated system, total energy always remains constant; this is known as the law of conservation of energy. In other words, energy can be neither created nor destroyed, and it can only transform into different forms. In particle collisions (classical mechanics), the sum of the particles’ kinetic energy before the collision is equivalent to the sum of the particles’ kinetic energy after the collision. The kinetic energy, depleted by an object slowing down as it moves upward against the gravitational force, is considered as being transformed into stored energy or potential energy. Later, it is transformed back to kinetic energy as the object speeds up in the course of its return to the ground.

2) Explain the energy conservation of a pendulum.

In the case of a simple pendulum, it swings upward and downwards. When the pendulum holds still briefly at the peak of its swing, the kinetic energy is practically zero, and the system’s entire energy components will be completely related to potential energy. When the pendulum knob comes back down, the potential energy is transformed back to kinetic energy. Every time the sum of the kinetic and potential energy is constant.

3) What is the effect of friction in the conservation of energy?

Friction slows down most physical mechanisms, especially motion (dissipating the energy constantly). The ideal conserved quantity is the sum of thermal, potential and kinetic energy. For example, when a box slips down a ramp, the potential energy becomes kinetic energy. When friction restricts the box’s motion to a stop, the kinetic energy is transformed into thermal energy. Just like the conservation law states, no new energy is created or annihilated. It only changes the form (it changes from potential energy to kinetic energy to thermal energy).

4) Give an example of energy conversion from chemical energy to kinetic energy.

A bus starts to move when the fuel’s chemical is transformed into kinetic energy (motion).

5) What is the significance of the special theory of relativity?

In classical physics, conservation of energy was different from conservation of mass. This conception drastically changed with the introduction of the special theory of relativity. It states that mass is directly related to energy by the equation

$$\begin{array}{l}hE = mc^2\end{array}$$
. This proves that the mass-energy as a whole is conserved. In other words, this shows that any system with mass can itself be transformed into complete energy and vice versa (only activates under extreme conditions).

6) The law of conservation of energy explains that the sum of all energy in an isolated system stays _____.

Explanation: The law of conservation of energy explains that the sum of all energy in an isolated system stays constant.

7) What is meant by energy?

Energy is the ability to do work.

8) When a shutter of a dam opens, _____ energy is transformed into kinetic energy.

Explanation: When a shutter of a dam opens, potential energy is transformed into kinetic energy.

9) What is meant by mechanical energy?

In a system, mechanical energy is the sum of both kinetic energy and potential energy.

10) What is the formula of mass-energy equivalence?

The formula of mass-energy equivalence is:

$$\begin{array}{l}E = mc^2\end{array}$$
.

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## Practice Questions

1) What is meant by kinetic energy?

2) What is meant by potential energy?

3) What is the relationship between kinetic energy and potential energy?

4) Give an example of chemical energy.

5) Give an example of thermal energy.

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