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Current time:0:00Total duration:2:34

CC Math: HSF.IF.C.7a

- [Instructor] We're told that Adam flew his remote controlled
drone off of a platform. The function f models
the height of the drone above the ground, in meters, as a function of time, in
seconds, after takeoff. So what they want us
to do is plot the point on the graph of f that corresponds to each of the following things. So pause the video and
see if you can do that, and, obviously, you can't
draw on your screen. This is from an exercise on Khan Academy, but you can visually look at it, and even with your
finger, point to the part of the graph of f that
represents each of these things. All right, so the first thing here is the height of the platform. So the drone is at the
height of the platform right when it takes off, 'cause it says Adam flew
his remote controlled drone off of a platform. So what is the time that he's taking off, the drone, or the drone is taking off? Well, that's going to
be at time t equals zero right over here. And what is the height of
the drone at that moment? It is 60 meters. So that must be the
height of the platform. So that point right over there tells us the height of the platform. And if they asked us what the
height of the platform is, it would be 60 meters. The next one is the
drone's maximum height. So then as time goes on, we can see the drone starts going to a higher and higher and higher height, gets as high as 80 meters. And then it starts going down. So it looks like 80
meters, at time 10 seconds, the drone hits a maximum
height of 80 meters. And then last but not least, they say the time when the
drone landed on the ground. Now, we can assume that the ground is when the height of the
drone is at zero meters, and we can see that that
happens right over here. And that happens at time
t equals 30 seconds. And so we've just marked it off, and I know what some of
you all are thinking. Wait, there's another time where the drone's height is at zero, and that's right over here. That's at negative 10 seconds. Couldn't we say that that's also a time when the drone landed on the ground? And this is a important point to realize, because if we're really trying to model the drone's behavior from time t equals zero, if t equals zero is
right when you take off all the way to it lands, then this parabola that we're
showing right over here, it actually, we would probably want to restrict its domain to positive times. And so this negative time
region right over here really doesn't make a lot of sense. We should probably consider
the non-negative values of time when we're trying to think about these different thins.