00:01
In this video, we're going to be looking at a quick example of two -dimensional kinematics.
00:05
So we have motion in two dimensions.
00:09
Okay, and what we have is we are flying a relief plane and we're trying to drop a package of food onto a small island.
00:16
This island is very small.
00:17
We can't land our plane on it, so i'll have to drop our package from the air and hope it lands on the island.
00:23
Okay, so we're flying directly horizontally with a velocity of my velocity of my plane.
00:30
Of 382 kilometers per hour or 106 meters per second and we're flying at a height h of 975 meters okay so we're 975 meters above our island which we're taking to be at sea level so our island is at a height of at zero meters okay and what we want to find is how long our package will take to fall once we drop it from the plane, how far away from the island we should drop it, and it's final velocity when it reaches the island.
01:12
So let me draw you a quick diagram before we start solving.
01:16
Okay, so we have our plane, and that's flying with our initial velocity, the initial in the x direction.
01:23
And here's just a quick coordinate grid.
01:25
That's positive x, positive y.
01:27
Right, we're going to drop the package, and it's going to travel in some parabolic trajectory until it reaches the island.
01:35
All right.
01:36
So we want to find this distance.
01:37
We want to find time.
01:39
And we want to find final velocity when our package lands on the island.
01:43
Okay.
01:43
Let's start with time.
01:44
We want to find the time that this package takes to drop from its initial starting position of 975 meters to its final position of zero meters.
01:54
This is in the vertical direction, of course.
01:57
We're going to use the equation y final equals y initial plus v initial times time plus one half acceleration times times squared.
02:08
Okay, and i have some numbers for this equation.
02:11
I know my final y position is going to be zero.
02:14
So i have zero equals my initial y position.
02:17
That's 975 meters plus v initial times time.
02:22
My initial velocity is entirely in the horizontal or x direction.
02:26
So my initial vertical velocity is zero.
02:29
So we can get rid of this term.
02:31
I know my acceleration is the acceleration due to gravity.
02:36
That's negative 9 .81 meters per second squared in the y direction...