00:01
Okay, so i have a toy rocket being launched from the top of a building 105 feet tall at an initial velocity of 163 feet per second.
00:11
So i've drawn the general form or written out the general form of a position function and now we're going to personalize it.
00:19
So for our problem, our initial velocity is 163 feet per second and our initial height is the height of the building 105.
00:28
So our function for part a will be s of t equals negative 16 t squared plus 163t because we're launching upward plus 105.
00:44
So that takes care of that.
00:47
Now in b, i want to know about maximum height.
00:52
Okay.
00:53
So maximum height is going to happen at the vertex of this parabola.
00:58
So the time for max height, i'm going to find by taking opposite of b, which in this case is 163 over 2a.
01:11
I'm finding the x coordinate of the vertex, opposite of b over 2a.
01:17
And when i do that, i'm going to get a time of approximately 5 .10 seconds.
01:26
Now, what max height is, well, that's the height i'm going to get when i put that 5 .1 seconds into my position function.
01:44
And that just becomes a calculator operation.
01:47
I find out that that is 520 .14 feet.
01:54
Okay.
01:57
In part c, i want to know for what time interval will the rocket be more than 433 feet? feet above ground level.
02:07
Okay.
02:08
So i'm going to set my function equal to 433.
02:22
I'm going to get everything on one side and zero on the other...