Work, Energy and Power

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In today’s class, we will be talking about work, energy and power. Enjoy the class!

Work, Energy and Power

What is work?

Work is said to be done when a body or object moves with the application of external force. We can define work as an activity involving a movement and force in the direction of the force. For example, a force of 30 Newton’s (N) pushing an object 3 meters in the same direction of the force will do 90 joules (J) of work.

Formula of work

When we kick a football, we are exerting an external force called F, and due to this force (kick), the ball moves to a certain distance. This disposition of ball from position A to B is known as displacement (d). This work is said to be done and can be calculated as W = F × d

Work = Force × Displacement = F × d

Unit of work

If a force of 5 Newton’s is applied to an object and it moves 2 meters, the work will be 10 Newton-meter. Newton meter in termed and Joules and it is the unit of Work (Nm).

Worked example

(1) An object is horizontally dragged across the surface by a 100 N force acting parallel to the surface. Find out the amount of work done by the force in moving the object through a distance of 8 m

Solution

We know that,

F = 100 N

d = 8 m

Since F and d are in the same direction,

θ = 0, [θ is the angle of the force to the direction of movement]

W = F Cos θ

= 100 x 8 x Cos 0

= 800 J [Since Cos 0 = 1]

What is energy?

Energy is the ability to perform work. Energy can neither be created nor destroyed. It can only be transformed from one kind to another. The unit of energy is same as of Work i.e. Joules. Energy is found in many things and thus there are different types of energy.

All forms of energy are either kinetic or potential. The energy in motion is known as Kinetic Energy whereas Potential Energy is the energy stored in an object and is measured by the amount of work done.

Types of energy

Some other types of energy are given below:

1. Mechanical energy
2. Mechanical wave energy
3. Chemical energy
4. Electric energy
5. Magnetic energy
6. Radiant energy
7. Nuclear energy
8. Ionization energy
9. Elastic energy
10. Gravitational energy
11. Thermal energy
12. Heat Energy

Unit of energy

The SI unit of energy is joules (J), which is named in Honour of James Prescott Joule.

What is power?

Power is a physical concept that has several different meanings, depending on the context and the information that is available. We can define power is the rate of doing work. It is the amount of energy consumed per unit time.

Formula of power

As discussed power is the rate of doing work. Therefore it can be calculated by dividing work done by time. The formula for power is given below.

P=Wt

Where,

P = Power

W = Work done

T = Time taken

Unit of power

As power don’t have any direction, it is a scalar quantity. The SI unit of power is Joules per second (J/s), which is termed as Watt. Watt can be defined as the power taken to do one joule of work in one second. The unit Watt is dedicated in Honour of So James Watt, the developer of the steam engine.

Worked example

(1) A garage hoist lifts a truck up 2 meters above the ground in 15 seconds. Find the power delivered to the truck. [Given: 1000 kg as the mass of the truck]

Solution

First, we need to calculate the workdone, which requires the force necessary to lift the truck against gravity:

F = mg = 1000 x 9.81 = 9810 N.

W = Fd = 9810N x 2m = 19620 Nm = 19620 J.

The power is P = W/t = 19620J / 15s = 1308 J/s = 1308 W. P=f.v

Summary

Work done is generally referred in relation to the force applied while energy is used in reference to other factors such as heat. Power is defined as work done per unit time.

What is work, energy and power?
Work
Definition	Work is said to be done when a force applied to an object moves that object.
Formula	We can calculate work by multiplying the force by the movement of the object. W = F × d
Unit	The SI unit of work is the joule (J)
Energy
Definition	In physics, we can define energy as the capacity to do work.
Formula	For the potential energy, the formula is P.E. = mgh
Unit	The SI unit of energy is joules (J), which is named in honour of James Prescott Joule.
Power
Definition	Power can be defined as the rate at which work is done i.e. energy converted.
Formula	The formula for power is P = W/t
Unit	The unit of power is watt (W).

 

In our next class, we will be talking about Units and Dimensions.  We hope you enjoyed the class.

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