Back to: PHYSICS SS1
Welcome to class!
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:
- Mechanical energy
- Mechanical wave energy
- Chemical energy
- Electric energy
- Magnetic energy
- Radiant energy
- Nuclear energy
- Ionization energy
- Elastic energy
- Gravitational energy
- Thermal energy
- 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.
Should you have any further question, feel free to ask in the comment section below and trust us to respond as soon as possible.
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great
how did you get Fcos0(theta)?
This is because the object moves along an horizontal distance
If it was a vertical distance it would have been
W=fsino times d
If a cage containing a truck of coal weighing 750kg is raised to a height of 90m in 1minute, what is the total power expanded. (g=10m/s
11250
where did you get F=mg = 1000 × 9.81
F=mg is the formula of force. 1000 is the mass given, 9.81 is the acceleration due to gravity(g)
9.81 represents the gravity although it was not given in the question. Most times gravity (m/s) is 10 and 9.81 can be approximated to 10 m/s.
Is there not supposed to be fundamental and derived units in the second week of first term
That 9.81 I don’t understand how you got it
I don’t understand too
Me too
In physics problems involving gravity (g) is commonly approximated as 9.8
The distance between the centers of mass of two objects affects the gravitational force between them, so the force of gravity on an object is smaller at the equator compared to the poles. This effect alone causes the gravitational acceleration to be about 0.18% less at the equator than at the poles. Acceleration due to gravity g varies all over the world. 9.81 was used for the example.
I also don’t understand how u got that 9.81
Hi everyone 😃You when we say gravity is equal to 10 m/s, It’s actually an approximation to make calculations easier the true gravity on earth is 9.81 m/s. As we level up we should make our calculations more Accurate.
Thank you
Thanks,it was so helpful.
An object is horizontally
dragged across the surface by a
200 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 5 m