 See many times what happens is that when the pressure comes, the pressure of exam comes, your expected performance suddenly goes down, okay? So you need to understand it is not because of your capability issue, it is only and only it's a psychological issue. So you need to have some confidence in yourself, okay? So don't lose hope or, you know, just remember that you were doing good when you've taken a lot of K-mon tests. So you need to just repeat your performance and get what you deserve, okay? So no need to get pressurized because J-mains is coming very close, all right? So these are the two questions, these two questions are just true and false statement. You need to check whether these two statements are true or false, okay? The first one, is it true or false? Okay, many are saying false, what about those who are on Skype? First one is true or false? Sir, not sure. Okay, this is the person, okay? Let's say this is the person sitting in a boat. This person is sitting in a boat, okay? Now how much volume of water it'll displace? It'll displace the volume of water whose weight is equal to the weight of boat and the man. Getting it? So if V-naught is the volume displaced, then rho V-naught G, which is the buoyant force is the mass of the person plus mass of the boat into G, can it out on this? Now if the person drinks some water, okay? It drinks let us say volume V1, okay? So if it drinks the volume V1 and let us say boat remains wherever it is, okay? So the level of this water has to go down if boat remains wherever it is because the amount of water in the pond has decreased because the man has drank some water, okay? But actually what happens is the mass of the man increases by mass of water it has drank, alright? So if the mass of the man increases by the mass of water it has drank, so how much extra volume of water it will displace from the pond in order to have the force balance? It will displace the extra volume of water displaced will be equal to the volume of water that is drank, getting it? Because now the buoyant force has to balance out more weight and the extra weight is coming because of water inside the stomach of the person, okay? So it has to displace now the same volume of water which it has drank, okay? So if the boat remains wherever it is then the water level will go down but what happens is that boat will occupy that extra volume of water that was taken out. So water level will remain wherever it was, okay? So this statement is false, right? So these kind of questions they are, you know, they have been asked many a times where the water level changes depending on different scenarios. So you need to be comfortable with answering such questions because they are the favorite questions of J question propositor. All of you understood this? Any doubt on the first one? If you don't have any doubts please proceed to the second one. Second one guys, any answer for the second one? So when the temperature is increased the tube will not expand, yes. And the second one is false. What happens when you increase the temperature density of mercury will reduce, it will become rho naught 1 minus gamma delta T, okay? So if this is the height of the barometer, height H then atmospheric pressure let's say Pa has to be equal to rho gh, okay? Now if let us say initially density is rho naught, height is H naught then since atmospheric pressure remains the same it has to be equal to the later on density which is rho naught 1 minus gamma delta T into g into new height h. Now g is unchanged, g doesn't change with temperature, okay? So density has reduced. In order to make sure that multiplication of this g and h remains Pa, h has to be more than H naught, fine? So that's how you have to solve this particular question. Any doubt on this one? See those routine type of questions which we have been dealing with when we were reading a chapter, it is like known to everyone. Everyone solves a question where there is a bucket, there is an object go and force acts on it, engine need to just balance the forces or when water is flowing in a pipe you just need to find the pressure or volume or volume flow rate, okay? Those are the like bare minimum or something which is known to everyone. So we need to force ourselves to identify questions which are different from others, okay? Then only you yourself will be different from others and you will be solving some of the unique type of questions, right? So when you practice any chapters questions make sure you don't look for how many questions you have solved but what are the varieties of questions you are solving because that is more important. Now can you do another question? I'll just draw a figure for that. So here is a question, draw with me. Now this is a pipe that is filled with water and let us say there is a lamp over here. So I have lit up a lamp which is heating one edge of this, okay? Let's say this is A and this is B. Water was completely filled earlier, okay? Now because of this lamp water begins to circulate and it will circulate in counter clockwise direction like this. You need to tell me whether it is true or false. This entire thing is vertical, okay? So gravity is acting downwards. This is gravity. Why? What is the correct answer? So it should be clockwise now because if you heat it then the particles will rise up. Why it will rise up? So because the particles rise up and the cold ones come down. See what happens is when you heat this part of the fluid, it becomes lighter, okay? This is denser. This is also denser. So when this becomes lighter, of course because of the gravity, the heavier particles will move down, okay? And this particle will go up, okay? When this moves up, then there is a flow from B towards A like this, okay? This is also called natural convection, okay? So that's how it will be. The flow will be actually clockwise, not anti-clockwise. Now another question, all of you. So you have a cube of ice. You have a cube of ice and you have, let's say, a metal piece inside. A small metal piece is inside the ice, okay? Now this ice is floating in the water. Ice is floating in the water, okay? Okay? Now everything is maintained at zero degrees Celsius, fine? The temperature is not changing during the entire process. It remains zero degrees Celsius only and now ice melts completely. Ice melts completely. You need to tell me what happens to level of water. This level will move up, go down or it will remain at that level only. Assume density of ice to be equal to density of water, okay? Purvik is saying it will remain at the same level. So I think you might have missed one small detail that metal piece is inside the ice. Purvik has retracted his message, but I have read it. Anyone? What is the answer? No one? Khushali is saying it will increase, the level will go up, Amoghi is saying it will decrease. Nishchal is saying increase, but slightly, okay? Let's see how we can do this question. Now consider the situation when metal piece is inside the ice. When metal piece is inside the ice, okay? One thing I think all of you can appreciate is that whatever is a change that is because of this metal piece inside. Had this metal piece not there, then everything will remain the same. But if this metal piece makes any difference, then only there will be some change in the level, okay? Now when metal piece is inside the ice and everything is floating, okay? By the way, I said density of ice considered to be equal to the density of water that is not correct. Otherwise, it will not float with the metal piece. So density of ice is actually less than density of water. But anyways, when ice melts, it becomes water with that density. Now coming back to this point about the metal piece. So when the metal piece, when metal piece inside the ice, how much volume of water it is displacing? Let's say volume of water is Vw and volume of metal piece is Vm. What do you think? Vw is greater than Vm, yes or no? Volume of water that is displaced by the metal piece because of the metal piece is greater than or less than volume of metal. So Vw is the volume of water that is displaced because of the metal piece, then the weight of the water displaced should be equal to the weight of the metal piece, right? And of course, metal piece has higher density, okay? So volume of water displaced will be more than the volume of the metal itself when it is floating because it has to balance the weight of the metal, right? But when the metal piece sank inside, then the volume of water displaced will be equal to volume of metal, isn't it? Because the metal piece will now sink, it will displace the same volume of water that is its own volume. So earlier it was displacing more volume, okay? Now it is displacing less volume, so the level will go down, okay? Fine, so we'll move to the next question in case you have any doubts, please type in quickly or you can speak up. Now we'll be taking regular objective type questions, single option correct right now. Try solving these questions. No Rithvik, okay, so we have seen question number one scenario many a times, all right? So here it is of no surprise that you're able to solve it quickly. So option C is correct over here. In fact, we use as a rule that horizontally pressure should not change. But if system is accelerating, then horizontally also the pressure will change. So if inside the water, if this is 2 and horizontally, let's say this is 0.1 at a distance x, then P2 should be equal to P1 plus rho Ax, okay? So horizontally pressure is changing. Now it means that pressure at 0.2 is more than pressure at 0.1, okay? So if I consider vertically, then pressure at 2 is P atmosphere plus rho G into H, this height. This height should be more than that height, then only pressure at 2 will be more than 1. That is the reason why the slope has to be like this. So option C is correct over here. Try solving the second one. So when I have taken properties of material, I have taken both flutes as well as solids for today. So at times you'll see properties of solids questions as well. Okay, two option A, everybody is saying, let's see how we can solve the second question. See whatever is the case, whatever is the dimensions, one thing remains constant. That is Young's modulus because the material is not changing. Young's modulus is what sigma by epsilon, okay? Now tension is same, okay? Now tension is same but stress could be different because of the surface area, sorry, because of the cross section area. So I can write sigma as tension divided by area. Now area I can write in terms of diameter because diameter is what is getting changed. So I'll be writing it as pi D square by 4 divided by epsilon. Let's say epsilon is change in length divided by original length L, fine? So Young's modulus into change in length divided by the original length is 4T divided by pi D square, okay? So delta L will come out to be equal to 4TL divided by pi into Y square, pi into Y into D square, all right? Now you can say that delta L is proportional to L by D square, okay? So whichever options L by D square is maximum, delta L will be maximum for that, okay? So for the first option, delta L is proportional to 50 divided by 0.5 square, which is coming out to be 200, okay? I'm not taking care of units here because when I compare, I'm taking same units for length and diameter everywhere. So this is 200, delta L by D square when you do for B, it will come out to be 100. It will be less than 100 for C option and D option. So I'll just pick option A here, okay? Now I'll take this opportunity to introduce a few things. So at times, you will have wire which is hollow like this, okay? So only this shaded portion has material, okay? And when you consider the area to apply for Young's modulus, you need to only consider this area which has material in it. So pi B square minus A square, if B and A are the radius, will be used as area of cross section, okay? To find this stress, all right? So we can move to the next one, right?