00:01
All right, so we've got a function for the height of a rocket based on the time t in seconds, and the height is measured in feet.
00:11
And first we want to find an expression for the velocity.
00:15
So velocity is going to be derivative of position.
00:19
So let's take a derivative using the power rule, minus 6t squared, plus 24t.
00:25
We're bringing the power down in front and then decreasing it by one.
00:30
Okay, good.
00:31
And then part b wants us to find the velocity at 0, 2, 4, and 6.
00:37
So we're looking for f prime of 0, f prime of 2, f prime of 4, and f prime of 6.
00:43
And we want to interpret those results.
00:44
Okay, f prime of 0 is 0.
00:48
So velocity is zero there.
00:49
This is probably takeoff.
00:53
We're not moving yet.
00:55
F prime of 2 is minus 24 plus 48 is 24.
01:03
So we're moving at 24 feet per second.
01:07
F prime of 4 is minus 96 plus 96.
01:17
Okay, so that's zero.
01:20
Okay, so what happens? this is probably at the peak.
01:25
We have a rocket on the ground.
01:29
We've taken off.
01:31
We're going fast here at two seconds.
01:34
And then at some point it doesn't go any higher.
01:38
So maybe we're actually out of fuel or something.
01:43
We stopped revving the engine...