 Hello, my name is Brad Langdell and are you a fan of like vintage things things from the past? Well, then you'll like this physics problem because you're gonna use some ideas from the past We're gonna talk about charge particles in uniform electric fields Those are probably new and we're gonna talk about a blast from the past projectile motion. This is a tough question It's got like 72 steps. So you can stop you can go back. You can check things out again if you need to Let's try it out So we've got a small positive charge and we know what the mass of the charge is five times ten to the negative four kilograms It's going at 350 meters per second into a parallel plate capacitor I'm gonna show you the picture for that here in a second. It kind of looks like this, okay? now the separation between the plates is 5.5 Centimeters and the potential difference between the places of the thousand volts Charge on that particle is positive three micro coulombs Assuming it starts right at the top of the capacitor How far from the entrance does it move before it hits the bottom? Now this is a pretty tricky question They've told you how far vertically this particle is gonna go it's gonna drop down through 5.5 centimeters What they want to know is how far does it go horizontally? And if you're looking at this and saying this diagram looks kind of familiar That's good because this is gonna go through Projectile motion it's gonna make up parabola in this uniform electric field And so this problem is gonna walk you through the steps for how to figure out how far this object goes horizontally how far it goes Displacement in the x direction kind of like we called it back in physics 20. Okay. There's my really horrible DX Okay, lots of steps the basic idea is very similar to everything. We've been working on in this unit So I've got my diagram drawn and labeled and I want to think a little bit about the fact that this is uniform motion in the x direction and Accelerated motion in the y direction classic projectile motion sort of stuff. Now if you're looking for some more Videos on projectile motion. I'll put a link to that so you can check it out here and see how to do that from back in physics 20 Now what I want to start doing is thinking a little bit about What have I got for variables? What can I work with here? What can I do with these variables? Well, the first thing I notice is I've got Potential difference and the distance between the plates if I take those two I can combine them to find the electric field strength Okay, so that's going to be my first little calculation I could do now I know that doesn't seem like it's gonna help me figure out how far this particle goes But it's something I could try and I would get a number and maybe it would help me out So if I take the potential difference of a thousand volts divided by the separation between the plates I get the electric field. Great. There's the electric field. This particles moving through maybe that will help somehow Okay, what can I do next? Well, I know electric field now and I know charge From electric field and charge I can go through and find electric force And so I've got a little calculation for that down there as well Again, it's kind of funny because you might think to yourself that electric force isn't gonna help me I'm not looking for the electric force. I'm actually looking for how far it goes But again, it's something you just kind of work out So here I went and worked it out and I found that if I substituted in the electric field and the charge On that particle I could find the electric force the particle moves through Okay, well now what can I do? I know force and I know mass Thinking back to physics 20 force and mass fit into Newton's second law and allow me to go through and do a calculation to find Acceleration so I substituted into Newton's second law the force that I just calculated along with a mass the particle I found its acceleration now This is going to be its vertical acceleration again because the y dimension is the accelerated dimension and the x dimensions Just uniform motion. So I know the acceleration in the y direction Okay, what can I do for with acceleration in the y direction and how far the particle moves in the y direction? Well, this is where physics 20 comes in handy I can calculate how long it takes the particle to move through these parallel plates I'm using a kinematics formula here And this is the same kinematics formula we used back in physics 20 d equals v it plus one half at squared The initial velocity in the y direction is zero is not 350 that's the x direction. We're talking about the y direction here the vertical the accelerated motion So I put a zero in for that velocity. I know how far the particle is going to move vertically point zero five five meters I know the acceleration vertically and I can go through and solve for the time zero point zero three one eight seconds Now we're getting somewhere because if I know how long the particle is in this electric field for I can now go And do my uniform motion in the x direction. I can calculate how far it goes into the capacitor Here I'm using the uniform motion formula v equals d over t. I just rearranged it d equals v times t multiplied the Horizontal speed and the time figure out how far it goes in That's a lot of steps And so one of the things I'm thinking through and I'm working these problems is not necessarily What are all the steps? I have to do all at once. I'm just doing one little thing at a time Baby steps. I'm trying to figure out one variable from another and just seeing where that path leads me It takes practice, but with a bit of practice you can get pretty good at these kinds of problems For more problems like this and for some notes on this as well. You can check out my website www.ldindustries.ca