"Find this stuff." And you're just gonna have to know that okay, if I run off of a cliff horizontally or something gets shot horizontally, that means there is no vertical velocity to start with, I'm gonna have to plug this initial velocity in the y direction as zero. Don't fall for it now you know how to deal with it. But we can't use this to solve directly for the displacement in the x direction.
So we want to solve for displacement in the x direction, but how many variables we know in the y direction? We need to use this to solve for the time because the time is gonna be the same for the x direction and the y direction.
It means this person is going to end up below where they started, 30 meters below where they started.
So this has to be negative 30 meters for the displacement, assuming you're treating downward as negative which is typically the convention shows that downward is negative and leftward is negative.
And let's say they're completely crazy, let's say this cliff is 30 meters tall. This is a classic problem, gets asked all the time.
And if you were a cliff diver, I mean don't try this at home, but if you were a professional cliff diver you might want to know for this cliff high and this speed how fast do I have to run in order to avoid maybe the rocky shore right here that you might want to avoid.- [Instructor] Let's talk about how to handle a horizontally launched projectile problem.These, technically speaking, if you already know how to do projectile problems, there is nothing new, except that there's one aspect of these problems that people get stumped by all of the time.So a lot of vertical velocity, this should keep getting bigger and bigger and bigger because gravity's influencing this vertical direction but not the horizontal direction. V initial in the x, I could have written i for initial, but I wrote zero for v naught in the x, it still means initial velocity is five meters per second.And we don't know anything else in the x direction.We don't know how to find it but we want to know that we do want to find so I'm gonna write it there. We know that the, alright, now we're gonna use this 30.You might want to say that delta y is positive 30 but you would be wrong, and the reason is, this person fell downward 30 meters. They started at the top of the cliff, ended at the bottom of the cliff.This vertical velocity is gonna be changing but this horizontal velocity is just gonna remain the same. In other words, this horizontal velocity started at five, the person's always gonna have five meters per second of horizontal velocity.So this horizontal velocity is always gonna be five meters per second.So this person just ran horizontally straight off the cliff and then they start to gain velocity.So they're gonna gain vertical velocity downward and maybe more vertical velocity because gravity keeps pulling, and then even more, this might go off the screen but it's gonna be really big. What we know is that horizontally this person started off with an initial velocity.