Okay, one more example with the momentum principle. And this one's kind of cool. Not necessarily the best way to do it. I mean, you're going to see there's lots of ways to approach a problem. Normally, if I know something about the time, it's very simple. Those problems with the robot, I was firing the rocket for one second, two second. That's very appropriate for momentum principle. In the dropping the ball, I knew the height. A little more work to find what I needed, but I could still do it. So this is one of those cases where later you'll see a better way to do it. Okay, this is actually something interesting and not the best way to do it. But in the movie Iron Man, Iron Man, Tony Stark, I hope I'm not spoiling stuff for you, but it's from the comic books too. So it's official lore. So I'm not spoiling anything. So he builds a suit and to escape his captors. And it's got rockets on it and it kind of works. And he shoots up really high in there and he falls down and crashes and makes a crater. And so here he is. And he's moving down. And I'm just going to say V equals negative 50 meters per second Y hat. And he's going to hit the ground. And when he does, he makes a crater. And so this is where he stops. Like that. And let's say this crater is a depth of D. And so you know you can imagine it probably maybe meter. I don't know, but that's the distance over which he stops. So what I want to do is calculate the net force on Iron Man while he's stopping. Okay, so if I want I could draw a free body diagram for him. Let me do it right here. I have gravity. And but since he's moving down, I'm going to need a very large force pushing up. I'll call this F in from the ground. But then we'll have a net force going up. Because the momentum was down and then it was momentum was zero. So the net force has to be this way. So I don't really need F in. I'll show you that we'll get it in a way. But I'm just going to calculate the net force. F net delta P over delta T. Okay, and so he has to ask us something too. Let's say it's, well he's got that suit on. Let me say 100 kilograms. Okay, so I'm just dealing with one-dimensional problem here. So I could say F net y is delta P y over delta T equals M times the final velocity in the y direction is zero minus the initial velocity in the y direction, which is negative 50. So I get that. That's going to be positive 50 over delta T. And again we get the same problem, but I just don't know time. Okay. So here again, if I assume that it's a constant force, I could say V average y over delta T. And that's also equal to V2y plus V1y over 2. So I can use this to get delta T. Okay, so my final velocity is zero. So I, and my delta y, it goes from, let's call this y equals zero to here, a negative D, I'll just write it out. It's going to be final of negative D minus zero over delta T. It has to be negative because he's moving down. And that's going to be negative 50 over 2. So delta T is going to be positive. Delta T is going to be negative D over negative 50 times 2, so it's 25. Okay. So now I can just put that in here and I'll get my net force. So let's put in everything we know. I have 100 kilograms. I have 50 meters per second. And then delta T is going to be a D, which, let me say it's a 1 meter. And then I have multiply by 25 meters per second. I'm running out of room here. Okay. Now, I want to check the units. I get meter squared per second squared over meter, meters per second squared times kilogram does give me units of force. Okay. So let's see. I was going to do it in my head, but I don't want to make my stake. I'll just do it in the calculator real quick. Okay. So let's see. 100. Oh, that's easy. Okay. 125,000 newtons. And let's just compare that to the gravitational force on Iron Man, which would be 980 newtons. Right? This times 9.8. So mg is 980 newtons. No. 9000. 9.8, that's right. 980 newtons. So if you wanted to calculate the 4c, or the zirts on them during this time, you could ignore gravity if you wanted to, because other ones are much larger. Okay. But they... Now, if you want to search for this on my website, I have a post about this where I look at this exact situation from a different standpoint. I use something else. But the end story is the acceleration of Iron Man is so large. It doesn't matter if this would be the suit it is. He's still going to be accelerating the same amount inside and he'd probably die. So that'd be bad. Okay.