Work, Energy and Power - Definition, Examples, Formula, Units, FAQs

Work Energy and Power Class 11 Introduction:

In physics, power work and energy has almost the same meaning, which must not be confused with everyday meaning. Let us understand this concept of work energy and power with the help of an example when we lift a box full of stuff; we get tired and we need to eat food to get more energy. Thus, we can say that the work transfers energy.

Work: Definition, SI unit, Example and What is the formula for work?

Work Definition: Work is said to be done when the force acting on the body and the body moves through some distance in the direction of force.

This work is said to be done on a body if it satisfied the below two conditions:

1. A force must act on body.

2. The object should move in the direction of force.

SI unit of work or work done unit or Work units: The SI unit of work is Joule (J).

Examples of work done: a man climbs up the hill, a horse pulls a cart; an engine pulls a train etc.

Work done Formula:

Work formula Physics is given by

W=F*d

Where, F is component of the force and d is magnitude of displacement.

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Nature of the work done:

self-drawn using Ms word

Work done, is a scalar quantity and its magnitude may be positive, negative or zero.

1. Positive work: When force(applied) along with displacement which are in the same directions then, the work done on the object is said to be positive work. For example: when a horse pulls the cart, the cart is displaced in the direction of force applied.
2. Negative work: When the applied force and the displacement are in the opposite directions then, the work done on the body is said to be negative work. For example: when we apply brakes to a moving bicycle the work done by the brake is negative because the braking force and the displacement act in opposite directions.
3. Zero work: When the body gets displaced along a direction perpendicular to the direction of applied force then, the work done on an object is said to be zero work. For example: The work done in pushing an immovable wall is zero, because displacement of the wall is zero. So, work done is zero.

Energy: Definition, Dimension, Unit and Formula.

Energy Definition Physics: Energy of a body is defined as its capacity or ability to do work.

Energy is a scalar quantity.

Dimensional formula of energy: [ ML2T-2]

SI unit of energy: joule (j)

What is the formula of energy?

Energy Equation: Change in K.E. = Final K.E. – Initial K.E.

Some characteristics of Energy:

1. The entire masses/matter possesses energy.
2. Energy can neither be created nor be destroyed; it always remains conserved.
3. Energy can be stored and transferred from one form to another form.
4. Some energy transfers or energy transformations can be seen, heard, or felt.
5. Total quantity of the energy in the universe exists is constant.

Energy has several forms: mechanical energy, sound energy, heat energy, thermal energy, light energy, nuclear energy, chemical energy, solar energy, magnetic energy etc.

Mechanical Energy: The energy produced by mechanical means is called mechanical energy. Let discuss the two forms of mechanical energy:

1. Kinetic energy: The energy possessed by the body by the virtue of it’s motion is called the kinetic energy.

Kinetic energy formula physics:

k=1/2mv²

Also we can say that the kinetic energy of a body is equal to one-half product of body mass along with square of its velocity.

Example of kinetic energy: A bullet fired from a gun can hit the target on account of the kinetic energy of the bullet. Wind mills work on the kinetic energy of the air. Ships sail using the kinetic energy of the wind. Water mills works on the kinetic energy of the water.

2. Potential Energy: The energy possessed by body with principles of its position. For example; potential energy of food is converted into electrochemical energy to operate our body system. Potential energy can be stored in an object by compressing them, stretching them, bending them. When we stretch the bow and release it the arrow goes forward with a large velocity on account of potential energy of the stretched bow.

Work energy and power Theorem for a constant force

Work-Energy Theorem Statement: According to this theorem the work done on a body by the net force is equal to change in kinetic energy of body.

Proof of work-Energy Theorem:

Suppose a constant force F is acting on a body of mass m produces acceleration a in it. After covering distances, suppose the velocity of the body changes from u to v.

Use the equation of motion,

v2-u2=2as

Multiplying both side by 12m

12mv2-12mu2=mas

By Newton’s second law,

F=ma

Therefore,

12mv2-12mu2=Fs=W

Ki-Kf=W

Change in the kinetic energy of the body = work done on the body

Hence, the work-Energy theorem proves for a constant force.

Also Read:

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Power Physics

Power: definition, dimension, unit.

Power Definition Physics: Power is outlined because of the rate of doing work.

P=W/t

Power is the scalar amount because it is the magnitude relation of 2 scalar amount.

Dimensional formula of Power: [ML^2 T^(-3)]

SI unit of power: Watt (W).

One Watt: the ability of AN agent is one watt if work done on the object is one joule per second.

one watt=(1 joule)/(1 second)

Instantaneous Power: We are able to outline the instantaneous power after limiting the average power as the interval approaches zero.

Also check-

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NCERT Physics Notes:

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