In classical mechanics, kinetic energy is the energy due to motion. It is stated as the work required to accelerate an object of a specific mass from the rest position to the stated velocity. As it accumulates energy during its acceleration, the object sustains this kinetic energy until its speed changes. The exact quantity of work is done by the object when slowing down from its current speed to a condition of rest. The kinetic energy of a linear body of mass m moving at speed v is:
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\(\begin{array}{l}K_{E} = \frac{1}{2}mv^2\end{array} \)
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Where m is the mass of the object and v is the object’s velocity.
This formula is true only for low to relatively slower speeds with respect to light speed. In relativistic mechanics, this is a valid estimation only when the speed is much less than the light speed. When the object’s speed approaches the speed of light (299,792,458 m/s), the object’s mass increases and relativity laws must replace the classical laws of mechanics. The relativistic version of kinetic energy is equal to the rise in the mass of a body over which it possesses at rest state, multiplied by the square of the light speed.
The SI unit of energy is the joule (J). A body with a 1kg mass travelling at a speed of 1m/s has a kinetic energy of 1J. On the subatomic scale, units like electron volts are used.
For a rotating system or body, rotational kinetic energy is equivalent to one-half product of the rotational inertia and magnitude of the square of the angular velocity.
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\(\begin{array}{l}E_{rotational} = \frac{1}{2}I\omega ^2\end{array} \)
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Where ‘I’ is the moment of inertia and ‘ω’ is the body’s angular velocity.
Ultimately the total kinetic energy of a system or an object is equal to the sum of all the kinetic energies generated from each form of motion.
The video explains the basic concepts of potential energy and kinetic energy.
Important Kinetic Energy Questions with Answers
1) What is meant by kinetic energy?
In classical mechanics, kinetic energy is the energy due to motion. It is stated as the work required to accelerate an object of a specific mass from the rest position to the stated velocity. As it accumulates energy during its acceleration, the object sustains this kinetic energy until its speed changes. The exact quantity of work is done by the object when slowing down from its current speed to a condition of rest.
2) What is the formula for kinetic energy?
The kinetic energy of a linear body of mass m moving at speed v is:
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\(\begin{array}{l}K_{E} = \frac{1}{2}mv^2\end{array} \)
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Where m is the mass of the object and v is the object’s velocity.
3) Explain kinetic energy in relativity.
The classical formula of kinetic energy is true only for relatively slower speeds with respect to light speed. In relativistic mechanics, this is a valid estimation only when the speed is much less than the light speed. When the object’s speed approaches the speed of light (299,792,458 m/s), the object’s mass increases and relativity laws must replace the classical laws of mechanics. The relativistic version of kinetic energy is equal to the rise in the mass of a body over which it possesses at rest state, multiplied by the square of the light speed.
4) What is the SI of kinetic energy?
The SI unit of energy is the joule (J). A body with a 1kg mass travelling at a speed of 1m/s has a kinetic energy of 1J. On the subatomic scale, units like electron volts are used.
5) What is the kinetic energy of a rotating body?
For a rotating system or body, rotational kinetic energy is equivalent to one-half product of the rotational inertia and magnitude of the square of the angular velocity.
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\(\begin{array}{l}E_{rotational} = \frac{1}{2}I\omega ^2\end{array} \)
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Where ‘I’ is the moment of inertia and ‘ω’ is the body’s angular velocity.
6) The total kinetic energy of a system or an object is equal to the sum of all the kinetic energies generated from each form of _____.
Answer: motion
Explanation: The total kinetic energy of a system or an object is equal to the sum of all the kinetic energies generated from each form of motion.
7) Which mechanical energy exists in moving bodies?
Kinetic energy exists in moving bodies.
8) Which mechanical energy exists in an object suspended on a spring?
Potential energy exists in an object suspended on a spring.
9) Which of the following objects has more kinetic energy?
- A bus stationed at a park.
- Water inside a dam.
- A rocket on a launchpad.
- A person riding a bicycle.
Answer: d) A person riding a bicycle.
Explanation: When an object moves, it acquires kinetic energy.
10) Friction directly opposes the relative motion between two objects. Therefore, it reduces the ______.
- Thermal Energy
- Kinetic Energy
- Potential Energy
- Chemical Energy
Answer: b) Kinetic Energy
Explanation: Friction opposes physical motion. Kinetic energy is a byproduct of motion. It decreases when motion decreases.
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Practice Questions
1) What is meant by mechanical energy?
2) What is meant by potential energy?
3) What is the difference between potential energy and kinetic energy?
4) What is a joule?
5) Give daily life examples of kinetic energy.
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