 ## Physics

Learn the toughest concepts covered in Physics with step-by-step video tutorials and practice problems by world-class tutors

5. Projectile Motion

# Intro to Projectile Motion: Horizontal Launch

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concept

## Introduction to Projectile Motion 4m
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Hey, guys, for the next couple videos, we're really talking about projectile motion. This is a super important topic in physics. You absolutely will need to know how to solve problems. For now, there's a lot of different variations of problems and project on motion, and it might seem that there's different ways to solve them. So I'm gonna show you in this video. I'm gonna introduce you to the main types of project on motion that you'll see, and I'm gonna show you that to solve them. We're just gonna use equations that we've already seen before, so let's check it out. So project on motion is gonna happen whenever you taken object and you throw it and it moves into dimensions. That's the important part under the influence of Onley gravity. So we've actually seen something similar to this before when we studied one dimensional vertical motion. If you take an object and you throw it straight up, then it comes straight back down on along the same direction that you through it because it's under the influence of only gravity. It just moved purely up and down. What's different about Project on motion is that we're not going to throw something up and down. We're gonna give it some sideways velocity, whether we're throwing it perfectly horizontal, whether we're throwing it downwards or upwards. These air really the main types that you might see, but because we're forgiving, it's, um, sideways velocity. It doesn't just go up and down. Instead, it goes to the side while also falling because, just like in vertical motion, it's still under the influence of only gravity. So because it's moving sideways and up and down, it takes these two dimensional parabolic paths some other examples that you might see or where you throw in something downwards or even upwards. You might see situations where it returns to the same height or might go even to a lower height or even a higher height like this. But this is really it. These are all the different kinds of variations that you might see. All of your problems are gonna fall into one of these categories, so it's common through all of them Is that the acceleration and the only thing that's influencing this object is just gravity that acts vertically downwards. So we have these two dimensional parabolic path. So how do we solve problems or remember whatever. We have physics problems in two dimensions. Whether whether it's motion or vectors, we can always decompose them into one dimensional X and Y parts. It's no different for projectile motion. So we can do here is we can kind of break up this motion this parabola into the X and y axis here. So imagine that we have this object here. Let's call this point a and it moves to the ground, which is Point B. And if we could Onley move along the X axis, then what it would look like is, even though this is taking a parabolic path like this in the X axis, this object just moves from A to B like this. Now it's also moving in the Y axis, so from a it's also falling under the influence of gravity like this. So it's really just doing two of these motions at the same time, and that's why it looks like a parabola. We can actually do this for any other motion. I'm just gonna pick this one over here, so like, for instance, like a and then it goes up to some points. Let's call that be, Then it goes back down again. Let's call that point. C. You can just take this and break it up into its too one dimensional parts in the X and y. So if you Onley could move along the x axis, then in the X axis you just go from a to B to C like this in the y axis. If you'd Onley move along the y axis what this would project? I would look like it would go from a and then it would go up to be And then we go back down to see so would actually look a little bit like this would actually look exactly like this motion over here. So really, it's just these 21 dimensional motions that are happening at the same time. Now, why is this important? Because we take a look here. The Onley acceleration at this object experiences is just gonna be in the Y axis due to gravity. So when it comes to these 21 dimensional motions, projectile motion is really just a combination of horizontal motion where the acceleration in the X axis is equal to zero and vertical motion where the acceleration in the Y axis is equal to negative G. It's negative because we're always gonna be assume that the up into the right is positive and G acts downwards. So it's negative. Now, why is this important? Because when it comes to the equations that we use for project on motion, we're really just gonna be using combinations of motion equations and vector equations. Now, if the acceleration in the X axis is equal to zero, it actually simplifies a lot of our four equations here because the acceleration terms will go away. And these equations actually don't really are not really helpful to us in the third term, acceleration term goes away, Which means that the Onley equation that we're gonna use in the X axis for Project on Motion is just our equation for constant velocity. Now, in the Y axis where you have some acceleration that isn't equal to zero, it's actually equal to negative G. Then we're just gonna use our 3 to 4 equations of motion and that's really it. And the other thing is because we're moving from 1 to 1 dimension to two dimensional motion, we're all just gonna We're also just gonna need some general vectors. Equations? That's really it, guys, there's nothing new that we haven't already seen before how to dio. So let's go ahead and take a look at how to solve some problems.
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Problem

Which of the following quantities are constant during projectile motion?

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concept

## Solving Horizontal Launch Problems 8m
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Problem

A rock is thrown horizontally with a speed of 20 m/s from the edge of a high cliff. It lands 80 m from the cliff's base. How tall is the cliff?

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example

## Clearing the Net 6m
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