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Kinetic Energy - Definition, Examples, Formula, FAQs

Kinetic Energy - Definition, Examples, Formula, FAQs

Vishal kumarUpdated on 02 Jul 2025, 04:30 PM IST

Kinetic energy is the energy of motion, and it's a fundamental force that shapes our world. Whether it's a car speeding down the highway, a soccer ball flying through the air, or even the simple act of walking, kinetic energy is at play. It moves objects, tells us about their speed, and helps us understand the concept of momentum. By exploring kinetic energy, we can appreciate the beauty and simplicity of this powerful force and see how it influences our everyday lives

This Story also Contains

  1. Definition of Kinetic Energy
  2. Kinetic Energy Examples
  3. Formula of Kinetic Energy
  4. Unit of Kinetic Energy
  5. Types of kinetic energy
  6. Difference between Kinetic Energy and Potential Energy
  7. Solved Example Based On Kinetic Energy
Kinetic Energy - Definition, Examples, Formula, FAQs
kinetic energy

In this article, we are going to study kinetic energy, how it depends on the frame of reference, the work-energy theorem, and its relationship with linear momentum. This topic falls under the broader category of work, energy, and power, which is a crucial chapter in Class 11 physics. It is not only essential for board exams but also for competitive exams like the Joint Entrance Examination (JEE Main), National Eligibility Entrance Test (NEET), and other entrance exams such as SRMJEE, BITSAT, WBJEE, BCECE and more. Over the last ten years of the JEE Main exam (from 2013 to 2023), more than ten questions have been asked on this concept. And for NEET four questions were asked from this concept.

Let's read this entire article to gain an in-depth understanding of Kinetic energy.

Definition of Kinetic Energy

Kinetic energy meaning: it is the energy created by an object as a result of its motion. When an object is set to accelerate, it is imperative that specific forces be applied. Work is required to apply force, and once the work is completed, the energy is transmitted to the object, causing it to move at a constant velocity. The word kinetic meaning is something related to or resulting from motion. The energy transferred is referred to as kinetic energy in this case, and it is dependent on the speed and mass of the object.

Kinetic Energy definition

“The kinetic energy of an object is known as the energy obtained by the object because of its motion.”

Also read -

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This ebook serves as a valuable study guide for NEET exams, specifically designed to assist students in light of recent changes and the removal of certain topics from the NEET exam.
Download E-book

How does Kinetic Energy get transferred?

Kinetic energy is a type of energy that may be exchanged between objects and turned into other forms of energy. The yo-yo is an excellent illustration of kinetic energy transformation. When you first start playing with it, you should let it rest in your hand; at this time, all of the energy is stored in the ball as potential energy. When a person drops the yo-yo, the stored energy is converted into kinetic energy or movement energy. All of the energy in the ball is transformed into kinetic energy once it reaches the bottom of the yo-yo. As it returns to the hand, all of the energy is transformed back to potential energy.

Kinetic energy transform

There is a ball (Image-1) that has potential energy, when we dropped the ball (Image-2) the ball started falling and now it has Kinetic Energy.

Learn kinetic Energy Better from the Given Video Below

Commonly Asked Questions

Q: What is kinetic energy?
A:
Kinetic energy is the energy possessed by an object due to its motion. It is the energy of movement and depends on both the mass of the object and its velocity. The faster an object moves or the more massive it is, the more kinetic energy it has.
Q: What is the kinetic energy of an object at rest?
A:
An object at rest has zero kinetic energy. Kinetic energy is only associated with motion, so when velocity is zero, kinetic energy is also zero, regardless of the object's mass.
Q: Why does a moving car still have kinetic energy even when the engine is turned off?
A:
A moving car has kinetic energy due to its motion, regardless of whether the engine is running. The car gained this energy from the work done by the engine earlier. It will continue moving (and have kinetic energy) until friction brings it to a stop.
Q: Why do asteroids pose a threat to Earth despite their relatively small size?
A:
Asteroids pose a threat due to their extremely high kinetic energy. Even though they may be small, their enormous velocities result in massive kinetic energies that would be released upon impact with Earth.
Q: How does kinetic energy affect the pressure of a gas?
A:
The pressure of a gas is caused by the collisions of gas molecules with the container walls. Higher kinetic energy of the molecules (due to higher temperature) results in more forceful collisions and thus higher pressure.

Kinetic Energy Examples

Here are some daily-life examples of kinetic energy…

  • Moving car
  • Bullet from gun
  • Throw of a ball
  • Windmills
  • Running

Formula of Kinetic Energy

The kinetic energy is given by the following formula

$\mathrm{K.E}=1 / 2 \mathrm{MV}^2$

Where M is the mass of the object, V is the velocity of the object and KE is kinetic energy.

Related Topics,

Unit of Kinetic Energy

The SI unit of kinetic energy is the joule.

1 joule $=\mathrm{Kg} \cdot \mathrm{m}^2 \cdot \mathrm{~s}^{-2}$

The CGS unit of kinetic energy is erg.

How can we calculate Kinetic Energy?

We know that work done is written as …

W= f.d = m.a.d ……….(1)

We know that $v_f^2-v_i^2=2 a d, d=\left(v_f^2-v_i^2\right) / 2 a$
placing the value of ' d' in equation(1)

$$
\begin{aligned}
& \text { Then.. } W=m \cdot a \cdot\left(v_f^2-v_i^2\right) / 2 a \\
& =1 / 2 m\left(v_f^2-v_i^2\right) \\
& =1 / 2 m v_f^2-1 / 2 m v_i^2
\end{aligned}
$$

Commonly Asked Questions

Q: How does kinetic energy relate to the concept of power?
A:
Power is the rate at which work is done or energy is transferred. In the context of kinetic energy, power can be thought of as how quickly kinetic energy is changing. For example, a more powerful engine can increase a car's kinetic energy more rapidly.
Q: How does kinetic energy affect the damage caused by bullets?
A:
The damage caused by bullets is largely due to their kinetic energy. Despite their small mass, bullets have very high velocities, giving them substantial kinetic energy. This energy is transferred to the target upon impact, causing damage.
Q: How does kinetic energy relate to the concept of escape velocity?
A:
Escape velocity is the minimum velocity an object needs to escape a planet's gravitational field. It's determined by equating the object's kinetic energy to the gravitational potential energy needed to move infinitely far from the planet.
Q: Can two objects with different masses have the same kinetic energy?
A:
Yes, two objects with different masses can have the same kinetic energy. A less massive object moving at a higher velocity can have the same kinetic energy as a more massive object moving at a lower velocity.
Q: What role does kinetic energy play in nuclear fission reactions?
A:
In nuclear fission, the kinetic energy of the resulting fragments is a significant portion of the energy released. These high-speed fragments collide with other atoms, transferring their kinetic energy and heating the surrounding material.

Types of kinetic energy

Kinetic energy has five types

types of kinetic energy

  1. Radiant energy

It is a type of kinetic energy that is always in motion. Examples of radiant energy…

  • Ultraviolet light
  • Gamma rays
  • Beta ray
  1. Thermal energy

Thermal energy, often known as heat energy, is produced when atoms clash with each other. The following are some examples of thermal energy:

  • The warmth of the sun
  • A cup of hot milk
  • Explosion of firecrackers
  1. Sound energy

It is produced by vibrating an object, it always travels in the medium. It can’t travel by vacuum. Examples of sound energy are:

  • Tuning fork
  • Beat of drum
  • Sound of hor
  1. Electrical energy

The free electrons, both positive and negative in charge, provide electrical energy. The following are some examples of electrical energy:

  • Battery
  • Lightning
  1. Mechanical energy

The sum of kinetic energy and potential energy is known as mechanical energy.

Examples:

  • A moving truck
  • A rocket in orbit

Commonly Asked Questions

Q: What's the difference between translational, rotational, and vibrational kinetic energy?
A:
Translational kinetic energy is associated with linear motion of an object's center of mass. Rotational kinetic energy is due to an object's rotation around an axis. Vibrational kinetic energy is associated with the back-and-forth motion of atoms within molecules or solids.
Q: How is kinetic energy related to temperature in gases?
A:
In gases, temperature is a measure of the average kinetic energy of the molecules. Higher temperatures correspond to greater average kinetic energies of the gas molecules.
Q: What happens to kinetic energy in an elastic collision?
A:
In a perfectly elastic collision, the total kinetic energy of the system is conserved. The kinetic energy may be redistributed between the colliding objects, but the sum of their kinetic energies before and after the collision remains the same.
Q: How does kinetic energy change in an inelastic collision?
A:
In an inelastic collision, some kinetic energy is converted to other forms of energy, such as heat or sound. The total kinetic energy of the system after the collision is less than before the collision.
Q: Why do spacecraft need to shed kinetic energy when landing on a planet?
A:
Spacecraft need to reduce their kinetic energy when landing to avoid crashing. This is typically done through atmospheric drag, parachutes, or retro-rockets, which convert the craft's kinetic energy into heat or work against gravity.

Difference between Kinetic Energy and Potential Energy

Kinetic energy
Potential energy
The energy created by an object as a result of its motion is known as kinetic energy.The energy created by an object due to its position or state.
The formula of kinetic energy is
K.E=1/2 mv2		The formula of potential energy is mgh
Vibrational energy is an example of kinetic energy.Gravitational potential energy is an example of potential energy.

Commonly Asked Questions

Q: How is kinetic energy different from potential energy?
A:
Kinetic energy is associated with motion, while potential energy is associated with position or configuration. Kinetic energy is the energy an object has because it's moving, whereas potential energy is stored energy that can be converted to kinetic energy.
Q: How does air resistance affect the kinetic energy of a falling object?
A:
Air resistance opposes the motion of a falling object, causing it to lose kinetic energy. Some of the object's gravitational potential energy is converted to heat energy due to air friction instead of being fully converted to kinetic energy.
Q: How does kinetic energy relate to work?
A:
The work-energy theorem states that the net work done on an object equals its change in kinetic energy. When positive work is done on an object, its kinetic energy increases, and when negative work is done, its kinetic energy decreases.
Q: What's the relationship between kinetic energy and momentum?
A:
While both kinetic energy and momentum depend on mass and velocity, they are different quantities. Momentum is mass times velocity (p = mv), while kinetic energy is half mass times velocity squared (KE = 1/2mv²). Kinetic energy is a scalar quantity, while momentum is a vector.
Q: What happens to kinetic energy when an object stops moving?
A:
When an object stops moving, its kinetic energy becomes zero. The energy is typically converted into other forms, such as heat due to friction, sound energy, or potential energy if the object's position changes.

Solved Example Based On Kinetic Energy

Example 1: An athlete of mass 50kg in the Olympic games covers a distance of 100 m in 10 s. His kinetic energy can be estimated to be in the range

1) 2,000 J−5,000 J
2) 200 J−500 J
3) 2×105 J−3×105 J
4) 20000 J−50000 J

Solution:

Kinetic energy

k=12mv2
wherein
m→ mass
v→ velocity

Kinetic energy is never negative

Kinetic energy

Initial velocity = 0

Final velocity $=v_f$
$S=u t+12 \mathrm{at} 2 \Rightarrow 100=0+12 \times \mathrm{a} \times 100 \mathrm{a}=2 \mathrm{~m} / \mathrm{s} 2$
Maximum speed $(a)=20 \mathrm{~m} / \mathrm{s} 2$
Maximum K.E. $=12 \mathrm{mv} 2=12 \times 50 \times 400=10,000 \mathrm{~J}$
Maximum speed (a) $=20 \mathrm{~m} / \mathrm{s} 2$
Maximum K.E. $=12 \mathrm{mv} 2$

If it runs with constant velocity $\mathrm{v}=10 \mathrm{~m} / \mathrm{s}$
Then K.E. $=12 \times 50 \times 100=2500$
So it lies between 2500 to $10,000 \mathrm{~J}$.

Example 2: The average mass of raindrops is $3.0 \times 10-5 \mathrm{~kg}$ and their average terminal velocity is $9 \mathrm{~m} / \mathrm{s}$. Calculate the energy transferred by rain to each square meter of the surface at a place that receives 100 cm of rain in a year.
3. 5×105 J
2) 4.05×104 J
3) 3.0×105 J
4) 9.0×104 J

Solution:

Total volume of water in 1 m 2 area

$$
=1 \mathrm{~m} 2 \times 100 \mathrm{~cm}=1 \mathrm{~m} 3
$$


Total mass in 1 m 2 area $=\rho \vee=103 \times 1 \mathrm{Kg}=103 \mathrm{Kg}$

Kinetic energy $=1 / 2 \times 103 \times 92=4.05 \times 104 \mathrm{~J}$
Hence, the answer is option (2).

Frequently Asked Questions (FAQs)

Q: Why does a spinning ice skater speed up when they pull in their arms?
A:
This is due to the conservation of angular momentum. As the skater pulls in their arms, their moment of inertia decreases. To conserve angular momentum, their angular velocity must increase. This results in an increase in rotational kinetic energy, which comes from the work done by the skater's muscles in pulling in their arms.
Q: How does kinetic energy affect the flight of a boomerang?
A:
The flight of a boomerang involves complex interactions of kinetic energy. The initial kinetic energy from the throw, combined with the rotational kinetic energy and the aerodynamic forces created by its shape, result in its characteristic curved flight path and return to the thrower.
Q: What role does kinetic energy play in the process of nuclear fusion in stars?
A:
In stars, extremely high temperatures provide hydrogen nuclei with enough kinetic energy to overcome their electrostatic repulsion and get close enough for the strong nuclear force to take effect, enabling fusion. This process releases energy and is the source of a star's power.
Q: How does kinetic energy relate to the concept of momentum in collisions?
A:
While momentum is conserved in all collisions, kinetic energy is only conserved in elastic collisions. In inelastic collisions, some kinetic energy is converted to other forms. The relationship between kinetic energy and momentum is key to understanding and analyzing collision physics.
Q: Why does a trampoline "store" energy when you land on it?
A:
When you land on a trampoline, your kinetic energy is temporarily converted into elastic potential energy as the trampoline's surface stretches. This elastic potential energy is then converted back into kinetic energy as the trampoline springs back, propelling you upward.
Q: How does kinetic energy affect the design and function of shock absorbers in vehicles?
A:
Shock absorbers are designed to dissipate the kinetic energy of the vehicle's up-and-down motion. They convert this kinetic energy into heat through fluid friction, improving ride comfort and maintaining better contact between the tires and the road.
Q: What role does kinetic energy play in the function of a hydraulic press?
A:
In a hydraulic press, the kinetic energy of the fluid (usually oil) is converted into potential energy in the form of pressure. This pressure is then used to exert large forces. The work done by the press is ultimately derived from the kinetic energy input to the system.
Q: What happens to the kinetic energy of air molecules in a bicycle pump as the piston is pushed in?
A:
As the piston is pushed in, the air molecules are compressed into a smaller volume. This increases their kinetic energy, which is observed as an increase in temperature of the air inside the pump.
Q: How does kinetic energy relate to the concept of horsepower in engines?
A:
Horsepower is a measure of power, which is the rate of energy transfer. In the context of engines, it represents how quickly the engine can increase the kinetic energy of a vehicle. More horsepower means the engine can accelerate the vehicle more rapidly, increasing its kinetic energy faster.
Q: How does kinetic energy affect the impact force in sports like boxing or football?
A:
The impact force in contact sports is related to the change in kinetic energy over time. A punch or tackle transfers the kinetic energy of the moving athlete or body part to the opponent. The larger the kinetic energy and the shorter the impact time, the greater the force experienced.
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