Energy Questions

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Very Short Answers Questions [1 Mark Questions]

Ques. What is the correct sequence of energy change from one form to another in a thermal power station when coal is used for generating electricity?

1. Heat energy > Mechanical energy > Electrical energy
2. Heat energy > Chemical energy > Electrical energy
3. Chemical energy > Heat energy > Mechanical energy
4. Mechanical energy > Electrical energy > Heat energy

Ans. The correct answer is a. Heat energy > Mechanical energy > Electrical energy

Explanation: When coal is burned, the heat energy it releases causes water to turn into steam. This steam's thermal energy is turned into mechanical energy as it drives the turbine blades. The generators will eventually convert the mechanical energy into electrical energy.

Ques. What happens to the potential energy of the spring when it is stretched or compressed?

1. Remains constant
2. Decreases
3. Increases
4. Becomes zero

Ans. The correct answer is c. Increases

Explanation: Due to the work done on the spring as it is compressed or stretched out, its potential energy increases.

Ques. What kind of energy does a flying bird possess?

1. Potential energy
2. Chemical energy
3. Kinetic energy
4. Both potential and kinetic energy

Ans. The correct answer is d. Both potential and kinetic energy

Explanation: A bird flying possesses kinetic energy as well as potential energy. The bird maintains a certain type of constant velocity at a particular height in flight. Accordingly, potential energy is caused by changes in height, while kinetic energy is caused by horizontal motion at a particular speed.

Ques. When one proton and one electron are brought close together, what will happen to the potential energy?

1. Potential energy gets converted into kinetic energy
2. Potential energy remains the same
3. Potential energy increases
4. Potential energy decreases

Ans. The correct answer is d. Potential energy decreases

Explanation: The potential energy decreases as they get closer to one another because the work is done by the force of attraction between the electron and proton.

Ques. The temperature of water at the top of the fall will be different from the temperature at the foot of the fall.

1. True
2. False

Ans. The correct answer is a. True

Explanation: When water falls from a height, potential energy is transformed into kinetic energy, which causes the water's velocity to reach its maximum at the bottom of the fall. The velocity is quickly decreased to zero at the bottom of the fall, thus its kinetic energy is converted there into heat energy, raising its temperature.

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Short Answers Questions [2 Marks Questions]

Ques. Define energy.

Ans. The energy of a body is its capacity of doing work.

There are many forms of energy energy like heat energy, sound energy, nuclear energy, electrical energy, etc.

The SI unit of energy is Joule (J) and it is a scalar quantity.

Ques. What is kinetic energy?

Ans. Kinetic energy is the type of energy that an object or particle contains as a result of its motion.

The kinetic energy of a body is equal to the product of its mass, m, and one-half of its squared velocity, v i.e.

K.E. = 1/2 mv²

Ques. Define the law of conservation of energy.

Ans. The law of conservation of energy is one of the fundamental laws of physics. This law governs the microscopic movement of individual atoms during a chemical process. According to the law of conservation of energy, “The energy can neither be created nor be destroyed, it can only be transformed from one form to another".

Ques. What is thermal energy?

Ans. Thermal energy is a type of energy that occurs as the temperature rises. The change in temperature of an object is exactly proportional to its thermal energy. Thermal energy takes the form of heat. The more thermal energy a substance has, the hotter it is. The increase in thermal energy caused by increasing the temperature is due to the quicker motions of the substance's atoms and molecules.

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Long Answers Questions [3 Marks Questions]

Ques. What are the applications of kinetic energy?

Ans. The following are the applications of kinetic energy

• Cycling
• Walking and running
• Flying airplane
• When moving air strikes the blades of a windmill, it creates rotation, which leads to the production of electricity.
• When flowing water's kinetic energy strikes a turbine in a hydropower plant, the kinetic energy of the water is transformed into mechanical energy. This mechanical energy is subsequently converted into electricity.
• When a bowler holds a cricket ball in his hand, the ball's kinetic energy is 0 since it is at rest.

Ques. What is gravitational potential energy? Write the expression for gravitational potential energy.

Ans. Gravitational potential energy is the energy that an object has due to its location in a gravitational field. The most typical use of gravitational potential energy is for an object near the Earth's surface when the gravitational acceleration is expected to remain constant at around 9.8 m/s².

Gravitational potential energy is given by the formula

Gravitational potential energy, U = – GMm/r

Where

• M is the source mass placed along the x-axis.
• m is the test mass at infinity.
• r is the distance from the source mass at which the gravitational potential energy is determined.

Ques. What is the difference between kinetic energy and potential energy?

Ans. The following are the differences between the kinetic energy and the potential energy

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Very Long Answers Questions [5 Marks Questions]

Ques. A shooter fires a bullet of mass 100 g with a speed of 100 m/s on a soft plywood of thickness 4 cm. The bullet emerges with 10% of its initial kinetic energy. Find the emergent speed of the bullet.

Ans. Given

• The mass of the bullet, m = 100 g = 0.1 kg
• The initial speed of the bullet, v_i = 100 m/s
• Thickness of the soft plywood, d = 4 cm = 0.04 m
• Final kinetic energy is 10% of initial kinetic energy i.e. K.E_f = 10% of K.E_i

The initial kinetic energy of the bullet is given by

K.E_i = 1/2 mv_i²

⇒ K.E_i = 1/2 x 0.1 x 100²

⇒ K.E_i = 50 J

Let vf be final speed i.e. the emergent speed of the bullet, then the final kinetic energy is given by

K.E_f = 1/2 mv_f²

Since, K.E_f = 10% of K.E_i

⇒ 1/2 mv_f² = 10/100 x 50

⇒ 1/2 x 0.1 x v_f² = 10/100 x 50

⇒ v_f = 31.6 m/s

Ques. What are the forms of kinetic energy??

Ans. The different forms of kinetic energy are

• Radiant energy: Radiant energy is a type of kinetic energy, which is the physical energy produced by electromagnetic radiation. It is emitted by matter and spreads into the surrounding environment.
• Thermal energy: Thermal energy is sometimes referred to as heat energy. It is created by the kinetic energy of atoms colliding with one other.
• Sound energy: Sound energy is the energy produced by an object's vibration. It moves through the medium, but it cannot move across a vacuum or space since there are no particles to function as a medium.
• Electrical energy: Electrical energy is the power of an atom's charged particles to perform an activity or move an object. Electrical energy is produced by the passage of electrons from one atom to another.
• Mechanical energy: Mechanical energy is the sum of kinetic and potential energy. It cannot be produced or destroyed, but it may be transformed from one state to another.

Ques. What are the different types of potential energy?

Ans. The different types of potential energy are

• Elastic potential energy: Elastic potential energy is the potential energy held when an elastic object is stretched or compressed by an external force, such as spring stretching. It is the work done to extend the spring, which is proportional to the spring constant k and the distance stretched.
• Gravitational potential energy: It is the one that has an object due to the earth's pull. It increases with height. Because gravitational energy may interact with another bigger object, it is not only one.
• Electric potential energy: It is one with an object that changes depending on the electrical charge. It might be either electrostatic or magnetic. When a vehicle was touched, it released a small amount of electrostatic potential energy.
• Chemical potential energy: It is the one that stores an object based on the arrangement of two atoms and molecules. We know that atoms and molecules can be arranged differently depending on their condition. It is also determined by its physical characteristics. Molecules have chemical bonds that can trigger or prevent a reaction.

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