Sources of energy - class-VI

Fossil fuels are mainly comprised of hydrocarbons. Energy is trapped in the form of chemical energy. When fossil fuels are burnt, chemical energy is converted into heat energy.

Coal is a fossil fuel. Once it is burnt, it turns to ashes and can never be used again.

Hydroelectric energy, also referred to as hydroelectricity or hydropower, is the use of moving water to produce electricity. This power is generated by converting the kinetic energy of flowing water into mechanical and then electrical energy. This process involves the use of turbines, which consist of a set of blades. The moving water flows over the blades, causing them to turn. The blades are connected to a rotating drive shaft. The mechanical energy of the drive shaft is transferred to a generator through a gearbox. The generator uses the mechanical energy of the drive shaft to move an electric conductor (typically coils of copper wire) through a magnetic field, which causes electrons to flow through the conductor, generating electricity. The electricity is then fed into the electrical grid to be used in homes, businesses, and by industry.
Hence, the statement is true.

Answer is A.

It is because they are actually fossils. They are made of dead and decay matter buried under the earth for many years. The dead and decaying matter under great amount of pressure and temperatures turn into fossils and they both are used as fuels so it is called fossil fuels.
The fossil fuels we use today are actually formed from plants and animals that existed hundreds of millions of years ago. The reason there is a lot of concern surrounding the expenditure of these resources is because most of what we use today from fossil fuels, such as oil and coal are being depleted much faster than they can be formed, so there is a limited amount available.
Hence, the statement is true.

Fossil fuels are formed when plants and marine species are buried below ground and are subjected to immense pressure and temperature for thousands of years. Examples include coal, petroleum and natural gas.

While it is falling it has certain velocity,as kinetic energy is defined as the virtue of its state of motion it will have kinetic energy.As it is at certain height it will have Potential energy which is defined by virtue of state of its position.Hence ball has both potential and kinetic energy.

While rolling down from hill a body will have some Potential energy due to height wrt to ground and due to rolling it will have some Kinetic energy .As it will keep rolling down , Its PE will change into KE

An flying aeroplane required some work to be done against gravity to go upto that much height that work will be stored as potential energy of the body. Also aeroplane has some mass and moving with some velocity so has some kinetic energy also. 

Taking toe of the hill as refrence point so some work against the gravity is done to raise the body to top of the hill so it poses some potential energy equal to mgh where m is mass and g is acceleration due to gravity and h is vertical height.

Since the bird is flying is must be at some distance from the ground and Potential energy is present when there is some height associated with that object (Since P.E = mgh). Also  the bird has mass and thus gravity will be acted on it. Kinetic energy is present for an object if it has velocity.This a flying bird has both kinetic energy and potential energy.

There are two different forms of mechanical energy,

A loaded gun, a set mouse trap and a compressed spring are examples of elastic potential energy.

Sun gives out light, which is an electromagnetic wave. Several nuclear reactions take place in Sun's core and thus light is produced.

Mechanical energy is the energy that is possessed by an object due to its motion or due to its position. Mechanical energy can be either kinetic energy(energy of motion) or potential energy (stored energy of position). 

Total mechanical energy of the system is equal to the sum of kinetic energy of the system and the potential energy of the system.

Total energy of the body is the sum of potential energy and kinetic energy.

work done=PE+KE

In hydroelectric power plant following sequence of energy transformation take place, 

The mechanical energy E of the particle is the sum of its kinetic energy and potential energy at any point. At x = 2 m, U(2) = 10 + (2-1)^2 = 10 + 1 = 11 J. Given kinetic energy K = 8 J, the total mechanical energy is E = U + K = 11 + 8 = 19 J.

$\begin{array}{l} { \eta _{ 1 } }=60rpm=\dfrac { { 60 } }{ { 60 } } rps=1rps \ \therefore { w _{ 1 } }=2r{ \eta _{ 1 } }=2\pi  \ { \eta _{ 2 } }=\dfrac { { 360 } }{ { 60 } } rpm=6rps \ { w _{ 2 } }=2\pi { \eta _{ 2 } }=12\pi  \end{array}$

Coal is fossil fuel formed from remains of plants that lived and died millions of years ago.

All fossil fuels are non- renewable source of energy. Since coal is a fossil fuel so, it is a non renewable resource.

Sound is considered as a form of energy because it obeys the First Law of Thermodynamics which states that energy can neither be created nor destroyed but it changes from one form to another. Sound energy is produced when an object vibrates. The sound vibrations cause waves of pressure that travel through a medium, such as air, water, wood or metal. Sound energy is a form of mechanical energy.

Seaweed and other biomass can be processed through anaerobic digestion to produce methane, which is a useful fuel source.

Natural gas, petroleum, and uranium are non-renewable energy sources. Wood is a renewable biomass source, making it the odd one out.

Fuels that burns without smoke are also termed as smokeless fuels. Smokeless fuels include charcoal, liquid petroleum, biogas, coke and anthracite.

Producer gas is an industrial fuel gas consisting primarily of carbon monoxide and nitrogen gas, typically produced by passing air over red-hot coke.

Flowing water is a good source of energy. It is available at many places and has great energy providing capability.

Coal is a conventional source of energy.

Out of the given energy sources, methane gas and petroleum are too highly combustible fuels to be used for domestic purposes. Natural gas is safer than the other two fuels and is less hazardous too.

Solar energy is potentially an excellent source of energy and if utilized properly, it can provide energy solutions for many generations to come.

Flammable substances are those that can easily catch fire. Wood is a combustible organic material, whereas glass, iron, and copper are not flammable under normal conditions.

Non-renewable sources of energy are those that exist in finite amounts and cannot be replenished on a human timescale once consumed.

A good fuel should be safe, provide steady energy, and be environmentally friendly. All listed criteria are standard requirements for a good fuel.

A situation where the demand for the energy exceeds its availability or the supply resulting in a bottleneck effect, an increase in prices etc., is known as the energy crisis.

Energy can neither be created nor be destroyed. It can only be transformed form one form to the another. Energy once used up cannot be reversed to its original form.

Examples of conventional sources : wood, coal, fossil fuels.

Hotspots are the volcanic regions near the mantle of Earth.It is the sources of geothermal energy also called natural thermal geysers used to harness electricity.

Natural gas is a naturally occurring, flammable gas comprising largely of methane and other hydrocarbons. It is a source of fuel and formed underground.

Conventional sources of energy are those that have been used for a long time, such as coal, petroleum, and natural gas. Solar and wind are non-conventional or renewable sources.

A wind-energy map provides data on wind speed and direction in specific regions to assess potential for wind power generation, not rainfall or earthquakes.

Food provides the chemical energy that our bodies convert into muscular and other forms of energy through metabolic processes.