00:00 Good day everyone.

00:14 My name is Tabelo A.E. the physicist here for today.

00:19 The topic we are examining today is work, energy and power.

00:26 The lesson objectives are at the end of the lesson the students will be able to

00:31 one define and explain concept of work, states the unit of works,

00:37 define energy, states different types of energy,

00:41 explain mechanical energy and types, define potential and kinetic energy

00:47 as it relates to mechanical energy, then solve simple problems or needs.

00:55 Work, work is done on an object when you transfer energy to that object.

01:02 If one object transfer or gives energy to another,

01:06 the first object does work on the other objects.

01:10 For example, if we have a box and we have a boy

01:18 trying to push the box, that means the boy is performing work on the box.

01:25 It is giving energy to that, so that at the end of the day,

01:30 if there is relative movement between the boy and the object and the box,

01:35 we say the boy has performed work.

01:38 But in reality, if someone should just start at the point,

01:42 carrying the load or carrying the car and there is no movement,

01:46 that person as well as the physicist's concern has not done any work.

01:50 So for any work to take place, there must be application of force

01:56 or energy and at the same time, there must be displacement, that is movement

02:00 from one point to another.

02:03 And this brings us to the definition of work.

02:06 Work is defined as when the force moves the body through a distance

02:10 and it takes place in the direction of the force.

02:13 That is our simple definition for works.

02:16 In magnitude, work equals force, which is represented by F,

02:24 multiplied by distance in the direction of the force.

02:29 And that is displacement.

02:31 So that if our F equals force multiplied by displacement,

02:40 then the units of work is Newton-Meta

02:51 because our force is measured in Newton and our distance is measured in meta.

02:58 So that the units is Newton-Meta or Jews.

03:05 That's the units for work.

03:09 Now, an example.

03:12 A boy applied a force of 16 Newton to push a wheelbarrow

03:16 through a distance of 5 m, calculates the work done by the boy.

03:22 For us to do that, we bring out the parameters provided.

03:33 The force is 16 Newton and the distance is 5 m.

03:44 Applying our formula work equals force multiplied by

03:50 distance or displacement in the specified direction.

03:55 That would be 60 multiplied by 5.

04:00 And that is 300 Jews or 300 Newton-Meta.

04:14 Another example, where we have situations

04:24 in which a force is applied to a body

04:32 at an inclined angle theta.

04:38 The formula will change a little bit.

04:42 And that would be F multiplied by D

04:48 cos theta. Where theta equals angle of inclination

05:04 of the force?

05:10 And from here, don't drag a bag of bins

05:14 with the force of 800 Newton.

05:18 F equals 800 Newton.

05:25 The angle of inclination here is 60 degree.

05:35 And the distance, which is D, is 4-3 m.

05:44 Now, using our formula, W cos F D cos theta,

05:52 our F is 8 on grid multiplied by D, which is 4-3

06:01 cos 60 degree.

06:06 And that is 8 on grid multiplied by 4-3

06:12 multiplied by 0.5.

06:14 Since our core 60 degree is 0.5,

06:18 so we have 11,000 Jews or 16,000 Newton-Meta.

06:35 Another example, where we have a force of 18,000 Newton,

06:52 which moves a body through a distance of 17 m.

07:00 And the direction of the force.

07:03 Force to calculate the work done, that would be force

07:07 multiplied by distance.

07:09 And that would be 80 multiplied by 17 m.

07:14 And that is 1360 Jews or 1360 Newton-Meta.

07:24 These are the ways by which we can solve problems under work.

07:32 Like I explained earlier, we have our force inclined

07:35 at Angutita, which we have explained.

07:40 And another one is situation where we have a body,

07:48 raised to a particular height.

07:53 We have a body raised to a particular height, H.

08:00 And lifted the body, we are working against the law of gravity.

08:05 And as such, by the time the body is raised to a particular height,

08:10 the body has its own width, which is mg.

08:14 And the total work done will not be equal to the width,

08:19 which is w multiplied by height, to which the body is raised.

08:24 Therefore, our work done equals mg multiplied by h.

08:30 And that is mg h.

08:38 With this, we can take another example on it.

08:45 An ion bar of mass 10 kilogram is raised to a height

08:56 6 m above the ground, calculate the work done and lift the ball.

09:06 Bearing in mind that our solution due to gravity

09:09 is 10 m per second squared.

09:14 Now, the work done, the formula is mg h.

09:22 Our mass is 10. 10 multiplied by a solution due to gravity,

09:28 which is 10 multiplied by h, which is 6 m.

09:34 That means 100 multiplied by 6.

09:39 So that will be 600 joules.

09:43 That is how to calculate the work done.

09:47 When an object is raised to a particular height, h.

09:54 Now, energy, energy is the ability to do work.

10:01 It is a scalar quantity.

10:04 And the unit of energy is joule.

10:07 That is, energy is also measured in joule, like our work.

10:15 Now, types of energy.

10:18 There are different types of energy

10:21 and there are one tamar energy.

10:24 This form of energy reflects the temperature difference

10:27 between two bodies or system.

10:30 Take, for example, hot water and cold water.

10:35 The temperature difference between them,

10:37 most of the way, you pour hot water or cold water in hot water,

10:41 the hot water will supply heat to the cold water.

10:44 So that at the end of the day, the temperature of the cold water

10:47 is raised, while the temperature of the hot water

10:50 is reduced a little bit.

10:52 That's transfer of energy.

10:54 It's also called tamar energy.

10:57 Also, we have mechanical energy.

11:00 This is form of energy associated with movements

11:03 or location of an object.

11:05 And for mechanical energy, it is divided into two,

11:09 namely, potential energy and kinetic energy.

11:14 Another form of energy is nuclear energy.

11:20 This energy emanates from the changes in the nucleus

11:24 of an atom or from nuclear reactions.

11:27 Take, for example, bombing.

11:31 We'll talk about bomb fusion or fusion.

11:35 It is common knowledge that, when there is war,

11:37 there's always bombing of any mystery tree.

11:40 That's bombing the atoms.

11:43 That is, the uranium use as one of the material

11:47 inside an atomic bomb.

11:49 By the time there is breakage, they release

11:52 light amount of energy, which destroys human being,

11:57 buildings, vegetations, animals.

12:00 So, during that process, there's always fusion.

12:05 That's breaking out the bomb.

12:07 Energy are being released.

12:09 And some of these energy are what can be shallow to produce

12:13 light.

12:14 Then, apart from that, we talk about electromagnetic energy.

12:18 Electromagnetic energy is energy from light

12:21 or electromagnetic waves.

12:23 Take, for example, a travel lens ray, gamma ray,

12:27 all those ones constitute what we call electromagnetic energy.

12:32 Likewise, we have sonic waves.

12:34 Those are the sun produced, some plate.

12:37 The energy that comes from waves, sonic waves,

12:41 are associated with sonic waves.

12:44 Then, we have gravitational energy.

12:47 This is energy associated with gravity.

12:49 As it involves attraction, all the portion

12:53 between two objects, due to their masses.

12:56 Also, we have chemical energy.

12:58 This is energy given by a charge particles called electrons.

13:02 For example, lightning.

13:04 It's an example of electrical energy in nature.

13:08 Another form of energy is solar energy.

13:12 Solar energy, this is energy obtained from the sun.

13:16 Most especially, the situation we find ourselves in the country

13:19 today, where there is epiletic supply of power

13:23 by the power holding company or the Nepal.

13:27 Most home, going darkness.

13:29 But there is an alternative arrangement now under the,

13:33 on the federal government policy of energy for all.

13:37 We are solar energy.

13:39 Lights being powered by solar energy are very stored.

13:43 Most especially, in the rural areas for generation of lights.

13:47 Now, we want to talk about mechanical energy.

13:54 Like we explained earlier, mechanical energy

13:58 is known as motion energy.

14:00 And it relates to position and motion of an object.

14:05 For mechanical energy, it can be either kinetic energy

14:11 or potential energy.

14:14 When we talk about kinetic energy, that is energy

14:17 possessed by a body, by a virtual of its position.

14:20 When a body is moving, that particular body

14:23 has what we call kinetic energy.

14:26 But when an object is at rest, that particular object

14:30 possesses what we call potential energy.

14:36 Now, potential energy.

14:39 Potential energy, this is energy possessed by a body,

14:42 by a virtual of its position at rest.

14:46 If an object of mass M is raised to a particular height H,

14:51 the work done, w, against gravity by the weight of the body,

14:56 equals potential energy, equals weight multiplied by height.

15:07 That is, our potential energy equals the weight of the object,

15:15 multiplied by height, to which the body is raised.

15:20 And that is the weight of the body is Mg, then multiplied by height H.

15:27 So that the formula for calculating our potential energy is MgH.

15:39 Example,

15:46 A man lift a load of 15 kg through a vertical height of 8 meter.

15:52 What is the potential energy of the body?

15:57 In brackets, our solution is due to gravity G, equals 10 meter per second squared.

16:03 Now, in solving this, just like we state the formula,

16:08 potential energy equals MgH, where M is the mass of the objects.

16:16 G is associated to gravity and H represents the height to which the object is raised.

16:24 Now, our M equals 15 kg, our G equals 10 meter per second squared,

16:43 and our H equals 8 meter.

16:48 That means, in substitute of this value, we have 15 multiplied by 10 multiplied by 8.

17:01 And that would be 150 multiplied by 8, and that would be 1200 joules,

17:14 or 1200 Nm.

17:21 That is how to calculate the potential energy.

17:31 Another example.

17:35 A mango fruit of mass 1.5 kg is dropped from a height 40 meter above the ground.

17:43 If G equals 10 meter per second squared, calculate one, the potential energy before it is dropped.

17:50 And two, the speed before hitting the ground or striking the ground.

17:56 In solving this, for our potential energy, we have an example.

18:04 A mango of mass 1.5 kg is dropped from a height 40 meter above the ground.

18:11 If G equals 10 meter per second squared, calculate one, the potential energy before it is dropped.

18:18 Now, first to calculate our potential energy, we apply our formula M, G, H.

18:27 We are our M equals 10 solar, equals 1.5 kg, our G equals 10 meter per second squared,

18:44 and our H equals 40 meter above the ground.

18:52 Now, substituting the values, we have 1.5 multiplied by 10 multiplied by 40.

19:04 So, we have 600 joules as the potential energy of the mango before it starts dropping.

19:18 The other parts were expected to calculate the speed before hitting the ground.

19:24 For our calculated speed, 1/2 MV squared, which is the formula for kinetic energy equals M, G, H.

19:38 And the energy will calculate as potential energy is 600 joules.

19:51 That means 600 equals 1/2 MV squared.

19:59 Our MV squared equals 600 multiplied by 2.

20:08 That's 1.5, much multiplied by this squared equals 1,200.

20:15 This squared equals 1,200 divided by 1.5.

20:22 And our V equals, if this is 1,800, then our V equals square root of 1,800.

20:40 And finally, the speed before it's tried ground is 4 to 0.4 meter per seconds.

20:54 So, that is how to calculate the speed.

21:00 Now, kinetic energy.

21:06 Kinetic energy, this is energy possessed by a body by virtue of its motion.

21:12 That is, when the body is moving, the body possess kinetic energy.

21:17 Unlike our potential energy, where that energy is due to potential of rest of the body.

21:24 But the moment that object changes from rest and starts moving,

21:29 is the potential energy will be converted to the kinetic energy of the body.

21:36 And kinetic energy is a scalar quantity.

21:40 If an object of mass M moves with a speed of velocity V,

21:46 the magnitude of the kinetic energy, which is represented by K E,

21:52 equals 1/2 mass of the body multiplied by a square of the speed of velocity,

21:59 which the body is moving.

22:02 And M equals mass of the body.

22:10 And V is the velocity, which which the object is moving.

22:29 An example, an object of mass 5 kilogram moves with a speed of 10 meter per seconds,

22:46 calculates the kinetic energy of the object.

22:51 Now, if our kinetic energy is 1/2 M v square,

22:59 and from the question, our M equals 5 kilogram,

23:13 and our V equals 10 meter per seconds.

23:21 Now substituting the values,

23:27 now we have multiplied by 5, multiplied by 10 square.

23:36 And now we have multiplied by 5 multiplied by 100.

23:48 And we have multiplied by 500.

23:55 And that would be 250 joules.

24:01 That's how we calculate the kinetic energy.

24:05 Then another example of kinetic energy.

24:09 A bullet of mass 50 gram lives a gun with a speed of 400 meter per seconds.

24:16 Calculates the kinetic energy of the bullets.

24:23 From the question, the bullet has mass 50 gram,

24:31 which we are expected to convert is to kilogram.

24:33 And that would be 0.05 kilogram.

24:40 And the speed equals 400 meter per seconds.

24:50 Now, calculating the kinetic energy, using our formula,

24:57 half M v square, half multiplied by

25:04 mass of the bullets, which is 0.05 multiplied by 400 square.

25:15 That would be 0.05 multiplied by 160,000.

25:34 So we have 8,000 joules.

25:39 That is the kinetic energy of the bullets.

25:45 Evaluation, we are expected to define A,

25:56 work, B, energy.

26:03 Secondly, briefly explain five types of energy you know.

26:13 Thank you for watching.

26:15 My name is Mr. Bello AA.

26:19 Till next time.

26:26 (upbeat music)