Question

State the law of conservation of energy. Explain briefly with a suitable example. ​

Answer 1

Explanation:

Whenever energy gets transformed,the total energy remains unchanged. According to this law,energy can only be converted from one form to another,it can neither be created or destroyed. The total energy before and after transformation remains same. ... The energy of a freely falling ball is conserved.

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Answer 2

The law of conservation of energy can be seen in these everyday examples of energy transference: Water can produce electricity. Water falls from the sky, converting potential energy to kinetic energy. The cue ball loses energy because the energy it had has been transferred to the 8 ball, so the cue ball slows down.

Law of Conservation of Energy Derivation

Considering the potential energy at the surface of the earth to be zero. Let us see an example of a fruit falling from a tree.

Consider a point A, which is at height ‘H’ from the ground on the tree, the velocity of the fruit is zero hence potential energy is maximum there.

E = mgH ———- (1)

When the fruit is falling, its potential energy is decreasing and kinetic energy is increasing.

At point B, which is near the bottom of the tree, the fruit is falling freely under gravity and is at a height X from the ground, and it has speed as it reaches point B. So, at this point, it will have both kinetic and potential energy.

E = K.E + P.E

P.E = mgX ——— (2)

According to third equation of motion,

v2=2g(H–X)⇒12mv2=12m.2g(H–X)⇒K.E=12m.

2g(H–X)⇒K.E=mg(H–X)

K.E=mg(H-X)——– (3)

Using (1), (2) and (3)

E = mg(H – X) + mgX

E = mg(H – X + X)

E = mgH

Similarly, if we see the energy at point C, which is at the bottom of the tree, it will come out to be mgH. We can see as the fruit is falling to the bottom and here, potential energy is getting converted into kinetic energy. So there must be a point where kinetic energy becomes equal to potential energy. Suppose we need to find that height ‘x’ from the ground. We know at that point,

K.E = P.E

=> P.E = K.E = E2 ——– (4)

E2 is the new energy

Where, E = mgH2

H2 is the new height.

As the body is at height X from the ground,

P.E = mgX ——— (5)

Using (4) and (5) we get,

mgX=mgH2⇒X=H2

H2 is referred to the new height

Law of Conservation of Energy Examples:

• In Physics, most of the inventions rely on the fact that energy is conserved when it is transferred from one form to another. A number of electrical and mechanical devices operate solely on the law of conservation of energy. We will discuss a few examples here.

• In a torch, the chemical energy of the batteries is converted into electrical energy, which is converted into light and heat energy.

• In hydroelectric power plants, waterfalls on the turbines from a height. This, in turn, rotates the turbines and generates electricity. Hence, the potential energy of water is converted into the kinetic energy of the turbine, which is further converted into electrical energy.

• In a loudspeaker, electrical energy is converted into sound energy.

• In a microphone, sound energy is converted into electrical energy.

• In a generator, mechanical energy is converted into electrical energy.

• When fuels are burnt, chemical energy is converted into heat and light energy.

• Chemical energy from food is converted to thermal energy when it is broken down in the body and is used to keep it warm.