Work and Energy 02 | Energy | Kinetic Energy | Potential Energy | Class 9 | NCERT | Sprint 

📝Download Lecture Notes From PhysicsWallah App : bit.ly/2SHIPW6 🎯 Science group- t.me/joinchat/RYszj_1cAl8xEvnv 🎯 Social Science- t.me/joinchat/GCBE5bDgFdxrZeI8 🎯 Mathematics group- t.me/joinchat/GBbG4p5S_OVRV920 ----------------------------------------------------------------------------- 🗓️ Scheduled Syllabus For Sprint ( Class 9th ) released describing which topics will be taught for how many days. Available at PhysicsWallah App :bit.ly/2SHIPW6 •Duration:-1 month (Jan 2021 - Feb 2021) 🎉 Free Batch Exclusive on our RU-vid Channel : Physics Wallah Foundation - 9 & 10 •Batch Details : 1) Best Faculties across India for different Subject/Topics. 2) Complete & Relevant Syllabus Coverage of Class 9th within 1 Month - Fastrack January 4,2021- February 15,2021 3) Monday - Saturday : Scheduled Classes everyday. •Physics : Tuesday, Saturday •Chemistry : Wednesday , Friday •Mathematics : Monday, Wednesday, Friday •Biology : Wednesday , Thursday , Saturday •S.ST : Tuesday, Thursday, Saturday, Sunday 4) Scheduled Syllabus released describing which topics will be taught for how many days. Available at PhysicsWallah App :bit.ly/2SHIPW6 ----------------------------------------------------------------------------- OUR SOCIAL MEDIA PROFILES : ⭐Instagram Handle : instagram.com/physicswallah/ ⭐Facebook Page: facebook.com/physicswallah ⭐Twitter Account : twitter.com/PhysicswallahAP?s=20 ⭐ PW App on Google Play Store : bit.ly/2SHIPW6 ❤️ Padhai Karte Rahe, All The Very Best 👍

26:19 workdone came negative because the force applied on the object to stop it was in the opposite direction to the displacement of the object. THANK YOU VERY MUCH SIR! Your explanations are great.

26:29 ~ To stop the object, the force applied is in the opposite direction of object moving which creates a 180 degree angle, making the workdone negative.

I didn't know about this channel my sister told me about this channel and from that time I forgot all the other u tube channels 🤣😂😂

Who is watching this in 2024 😅

Bhagvaan jo bhi is comment ko like kre uske maa, baap ki umer bandha do

26:20 the force applied on the body and displacement is supplementary so cos180 degree and its value is -1, we will multiply 1120 by -1. so our ans will be -1120

Hw ans is 1- an object moving with constant velocity if we aply the force opposite of it then it come to rest then work done is negative 2- it's kinetic energy convert into heat energy and sound energy and also potential energy because it shape change due to collapse to earth. Because of these it produce sounds. 3- no

27:10 Workdone is 4mv square And per cent is 800 percent... Sir u teaches the best 👌....

king of physics @rakshaksir salute to the way of teaching and craking funny jokes in between make me smile everytime.... THANK YOU SIR

Sir you made my life so easy and make the physics enjoyable ❤you are amazing 👏 👏 ❤ I really like your teaching style you are mindbolwing sir 🎉

Work done is negative because force is acting oposite side of displacement... You are best teacher of physics love from uttrakhand

26:31 The work done is negative because when we apply force to stop the ball it's make a 180 degree and we know 180 degree is a part of negetive workdone.

26:20 , Sir..for example, Displacement right me tha, usko rokne ke liye force left me lagaya.. Toh dono ke bich ka angle 180° bann gaya.. And formula = F × s × cos. And Cos180 = -1 So, Answer negative me aaya 👍👍

Sir kyunki displacement" s "toh aage ja rha hai and jo force hai use rokne ke liye woh piche lg rhi h means retard kr rhi hai toh Wd = Fscos theta se jo angle bn rha h 180 degree ka h and cos 180 = -1 hota h toh WD negative m ajayega

Sir Work done is negative because the Force applied and the displacement that took place were in opposite direction and formed an angle of 180° . Now the value of cos theta 180° is -1 and Work = Force x Disp. x cos theta That is why work done is negative and it also means that it is a retarding motion.

Challengers 1)-mv²/2 2) Becomes zero 3) Because ground is considered zero level and pot energy = mass * g * height from ground and when object is placed on ground h = 0 So, mgh = m * g * 0 = 0

9:11 Sir, I was thinking about this method only but you are great and a legend in our term.

Too good man...idk what to say....u r the only teacher with whom I can read physics with intrest

26:33 Work done is negative because the force is applied to stop the body and it's opposite direction ❤️

Q1 - K.E Q2. Its K.E ----》P.E Q3. If the object h=0 from the ground and it is at rest so the. P.E + K.E. = Zero. And sir i have a doubt if we are in space so then also the object should have the P.E . And sir class is awesome 👌

50:17 yes sir you are right we apply force in upward direction we just decrease the amount of applied force in the upward direction.

Challenger questions : 1.) Workdone =-1/2mv^2. 2.) K.E=0 3.) It has no energy because it is on ground and it is taken as a reference point and also it is not moving...

%age change in kinetic energy = final K.E -Initial K.E /Initial K.E ×100

1.If force and displacement are in opposite direction, workdone called negetive 2. Angel between force and displacement is 180° 3. It will increase the speed (RETARDATION) 26:28

26:28 workdone is negative because the force is opposing the motion of the object. In other words work done is opposite in the direction of displacement.

Sir please explain Relationship between kinetic energy and momentum.

26:28 because we have to stop the particle and the angle between them is 180° and Cos 180° = -1

2-the PE that convert into KE is remain store in the obj according to its Height (Matlab PE is equal to the h of obj from the ground so when we fall it it's KE = to the PE and PE equal to the H of obj so, Jo PE he vo remain reh jae gi obj kyoki vo to KE change hue hi niii due to stop before touching the ground

-1125 J because the let object was moving(displacing) right side and we have to apply left side force (-1125 J WD) then the object will stop. Angle between them is 180 degree so negative WD

So nice lecture sir , love you sir , sir aap Jaan ho hamari , thank you so much sir , aap ki bahot help mil rahi hai , sir aap God gift ho sabke liye , sir all India apke sath hai , thank you sir from all India🙏

26:30 because in this case angle formed force and displacement is 180°🙏🙏

Question Number 2 work done is negative because the object displace forward and force is in opposite directions .So we know that when force and displacement are in opposite direction then there is negative work done and create angle of 180 degree.

i solved the olympiad lvl question aur kis kis ne kiya?? 🕉🕉🕉🕉

1.) 1/2* m/v² 2.) when object ready to fall it energy is "mgh" and as it fall it's potential energy convert into kinetic energy and increase in kinetic energy in increasing in it's velocity. When object touch the ground it's kinetic energy is in higher level and when object stops it's kinetic energy is become zero 3.) Yes ,an object on ground so it is not in motion so the kinetic energy is zero and object height from ground is zero so it's potential energy become zero and and sum of potential and kinetic energy is mechanical energy as both energy is zero mechanical is zero so every point of energy seen is zero

32:50 😂😂 26:23 Because the work is negative work and thetha is 180 degree and force is acting in opposite of displacement 28:00 sir answer is 800% Challenger question 1. -1/2 mv² 2. When object comes in contact with ground .energy conversion happens . Like sound energy , heat energy etc 3. No sir , If object is at rest on ground . Clearly it has KE,P.E(due to height) =0 . But sir the object can posses other forms of energy as well like P.E(due to configuration ) and also solar energy , wind energy , electric energy. Hence Energy =(not ) 0 .

Sir literally aap se physics padh ke bahut Maza aata hai aur har ek concepts ek hi baar Mai mind Mai set ho jaate hai. I'm you're great fan Sir ji.

Sir negative isliye aaega kyuki apn force lga rhe displacement ke against or angle bhi hoga 180degree isliye wd negative hoga...

Challengers:- 1. 1/2 * mv² 2. The KE will be absorbed by the ground. It will move it's molecules and will boost their sleed but it will be very less. 3. Depends, if the object is made up of matter then it's particles will have KE and if we choose different grounds then its PE will not be equal to 0

01:03:12 question 3. Yes the energy will be zero because of we know that kE=1/2mv^2 -1/2mu^2 and body is in rest. And there is no displacement.

26:24 when we stop a body moving with a velocity we need to applied energy in opposite direction of body

1)- the energy required to stop the object is -1/2*m*v^2. 2)- its all kinetic energy is converted into it's potential energy that follows the conservation of energy as sir will explain this topic on next lecture. 3)- yes, object placed on ground have zero energy because as our reference point is ground at zero level the height is zero so potential energy of an object is zero because of it's height which is zero. Hope it helps.

Sir , if a body is at rest ,it has zero kinetic energy.a train which is in motion it will have kinetic energy,but with reference to another train which is moving parallel and with equal constant velocity ,both of them will be at rest with reference to each other,in this case will kE will be zero?

26:26 Sir! Jahan se stop krenge uss place ka angle aur object ka position ka angle 180° form krega as dono ke direction opposite h, that's why!

40:03 😂 " Bccho karvayi to workdone se hi start hoti hai " 😂 Hats off to u sir ❤️

Because the force applied to stop is in opposite direction. so 180° formed and cosQ of 180° degree equal to -1

Sir, in the last challenger question of L1, why are we calculating the work done by force of friction by multiplying -5 and 10 because work done is calculated only in the direction of force applied although in this case displacement is not in the direction of frictional force

Sir you are amazing teacher of physics there is no sir like you.

26:26 Because force is in opposite direction and angle between force and displacement is 180 degree. That's why here's negative workdone.

In Concept Building question 2, Work done was negative because the angle between the force and the displacement was 180° and cos 180°= -1, you taught us about this in the first lecture

26:24 because the direction of force and displacement is opposite

workdone came negative because the force applied on the object to stop it was in the opposite direction to the displacement of the object. THANK YOU VERY MUCH SIR! Your explanations are great.

Can someone please explain to me how Is downward force the same as gravity? At 50:56 sir said that it will take the same amount of force to displace the object downwards as it took to displace the object upwards. I mean, if it took me to lift a 6 kg object with 10 newtons of force upwards, to bring it down, it should take less than 10 N of force.

Sir really l have seen so many teachers...but no one is like you.... really you are the best teacher...

We got the value of W.D in negative because 1. We are retarding the acceleration

49:42 sir hum smuggling nahi karte 😉

Sir I have an question : Is change in kinetic energy is equal to change in potential energy. MGHf - MGHi = Work done 1/2mv^2 - 1/2mu^2 = Work done Both RHS is same.

Concept building ques.2 The workdone is -1125 because we are applying the force in opposite direction of displacement so the angle will form 180° and 180° is the negative work so workdone is -1125. Thank you And sir you teach very nice😍

Concept : 2, In the work done the force we apply is in a direction but the displacement is in opposite direction, so the object decreases it's speed and becomes zero velocity and that is the negative work

Sir you are teching us like a legend............ Next level Explanation❤

So sad that I can’t understand the language but he had clearly explanation, love you teacher 👨‍🏫

41:45 Sir,In case if we are applying same force as earth then it will termed as balanced force and balanced force can't produce acceleration, then how is it possible to lift that object...🤔😊

😭😭😭😭 bahut bahut dhanayabad hame youtube ke jariye padhane ke liye.

26:38 because force applied to stop the car is in opposite direction of the car's displacement

I am studying this chapter again bcoz of class 11th and sir's lecture is super great op

Tomorrow is my exam I don't know how my paper of physics gone but when I find your channel now I understood all topics of chapter work power Energy thank you sir ❤️❤️❤️

Ans- 1) -1/2mv square 2) It becomes zero. 3) Yes, Because the ground is considered as a reference point which is equal to 0

26:25 workdone negetive me aaya kyoki force displacement ke opposite direction me apply kiya gaya hai object ko rokne ke liye

sir if we applied force equals to mg then how we lift an object because it became balanced force

Sir your explanation is very perfect i understand this chapter very easily thank you so much sir

Hats off to you sir ❤️ Thank you soo much for putting so much effects to teach us ❤️ 😊

ANS:- When an object falls freely, its potential energy gets converted into kinetic energy. When the object hits the ground, its kinetic energy gets converted into heat energy and sound energy. THIS EXPLANATION IS FROM MY TEACHER AND ANSWER IS FROM ME:-) Explanation:- When an object falls freely towards the ground, its potential energy decreases, and kinetic energy increases; as the object touches the ground, all its potential energy becomes kinetic energy. As the object hits the hard ground, all its kinetic energy becomes heat energy and sound energy. It can also deform the ground depending upon the ground’s nature and the amount of kinetic energy possessed by the object. Kinetic energy is a property of a moving object or particle and depends not only on its motion but also on its mass. Potential energy is stored energy that depends upon the relative position of various parts of a system

This is due to because both are vector quantities due to which one has to be in negative that makes the product negetive 😅 Or this is due it form 180 between force of ball and force to stop it 1125cos180°×0 = -1125

26:34 sir as there is 180 degree between applied force and the displacement means the F and S both are in opposite directions so workdone is negative

26:29 when force and energy are are in opposite directions....and the angle between them is 180°, then work done will be -ve

Negative because we applying force in the opposite direction of the displacement

There is negative work done because velocity has decreased

quality ?? only 480p

26:23 because the opp. Force acts on it and it moves forward, so, the angle between them is 180° and we know that cos180° = -1 so the fscos theta will be -fs which represents the negative workdone 😊😊

1- in order to bring the object to rest the work done must be equal to K.E of moving object =1\2 MV square 3- yes

Sir what if we apply force more than Mg(Mass*Gravity=weight) to lift object.

Thank you sir ... Your way of teaching is absolutely amazing. ...you have cleared all my doubts and confusion of this topic ... Once again thank you so much sir ...💜💜💜💜

Challengers Answer 1)-mv²/2 2) KE = !/2mv^2 here on collision v = 0, therefore KE = 0 but we known energy could not be destroyed. So, it would be converted into heat and sound energy 3) Because ground is considered zero level and potential energy = mass * g * height from ground and when object is placed on ground h = 0 So, mgh = m * g * 0 = 0 Love from kashmir ❤❤❤❤

1) -1/2mv^2 2) when a body will fall freely its potential energy will decrease and its kinetic energy will increase when it will touch the ground all its potential energy has been converted to kinetic energy and the kinetic energy will change to sound and heat energy 3) the kinetic energy will be 0 but the potential energy is relative term it depends person to person but for a given person the potential energy will be 0

The workdone came in negative because to stop that object person had to apply force against displacement so the angle between force and displacement would be 180 degree .

Ans for question asked 26:29 The Answer is , This Because sir the force applied to it is opposite to it something like retardation and we trying to stop it Bass sir itna hi pata tha mujhe jo bata diya meine Thanku😊😊

To stop the object the force is applied in opposite direction which makes 180° so that is why WD is negative

In concept building question number 2 - since the force required to stop the body acted in the opposing direction to that of its displacement, the angle between them will be 180 degree and we know that cos 180degree equals minus 1. Thus workdone came in negative

Q1. By the use of work energy theorem it can be done answer is -1/2mv^2. -ve as it is in the opposite direction of the Motion of the object Q2. It's kinetic energy changes to the sound and heat energy while hitting the ground while the total energy remains conserved Q3. No it has the internal energy of its body due to chemical reaction taking place inside the body (respiration)

Sir workdone came in negative because it is in negative y-axis as of Cartesian system. Lecture was amazing😃👏

The only thing I want to say is - "Best video ever 🔥🔥🔥🔥" salute you sir

27:33 formula is KEf - KEi

Sir is also a good Gym Trainor 😅

Change in kinetic energy is 4MV^2 and percentage change is 800%

Am i only one here who fell in love with physics because of, awesome teaching style of rakshat sir🥰..

Here,negative sign shows retardation or displacement in the opposite direction of the work done. Thank you so much for this amazing lecture👏

Homework questions (i) W= -1/2.m.v.v (ii)When the body comes to the ground it's final velocity becomes 0.then,when the object it at rest it's kinetic energy is 0. (iii) If a object at ground and if it's final velocity is 0 then it's kinetic energy is 0 or it's final velocity is non zero then it's kinetic energy is non zero. Thank you so much sir for the best explanation.My all concepts are clear😊😊😊😊thanx again😊😊😊🎉🎉🎉❤❤❤

26:27 = because force is acting opposite from the displacement as the question says it is stopping the moving object

sir thank you soo much for this wonderful lecture

26:31- it is negative because the work done is decreasing the speed which happens when force and displacement are in opposite directions