You might think 30 meters is the displacement in the x direction, but that's a vertical distance.This is not telling us anything about this horizontal distance.
You might think 30 meters is the displacement in the x direction, but that's a vertical distance.This is not telling us anything about this horizontal distance.So this person just ran horizontally straight off the cliff and then they start to gain velocity.
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 if something is launched off of a cliff, let's say, in this straight horizontal direction with no vertical component to start with, then it's a horizontally launched projectile. I mean a boring example, it's just a ball rolling off of a table.
If you just roll the ball off of the table, then the velocity the ball has to start off with, if the table's flat and horizontal, the velocity of the ball initially would just be horizontal. Let's say this person is gonna cliff dive or base jump, and they're gonna be like "whoa, let's do this." We're gonna do this, they're pumped up.
So if you choose downward as negative, this has to be a negative displacement. Well, for a freely flying object we know that the acceleration vertically is always gonna be negative 9.8 meters per second squared, assuming downward is negative.
Now, here's the point where people get stumped, and here's the part where people make a mistake.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.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.- [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.They want to say that the initial velocity in the y direction is five meters per second.I mean people are just dying to stick these five meters per second into here because that's the velocity that you were given. That's why this is called horizontally launched projectile motion, not vertically launched projectile motion. The initial velocity in the vertical direction here was zero, there was no initial vertical velocity.Maybe there's this nasty craggy cliff bottom here that you can't fall on.So how fast would I have to run in order to make it past that?