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  • - [Instructor] Katie throws a ball in the air

  • for her dog to chase.

  • The function f models the height of the ball, in meters,

  • as a function of time, in seconds, after Katie threw it.

  • And we could see that right over here.

  • This is our function f.

  • So at time t equals zero,

  • the height looks like it's a couple of meters.

  • And then as we go forward in time,

  • to a little under 2 1/2 seconds, the ball's going up.

  • And then after a little under 2 1/2 seconds,

  • the ball starts going down.

  • And after, by the time you get

  • to five seconds or close to five seconds,

  • it looks like the ball is on the ground.

  • Its height is zero meters.

  • So then they ask us

  • which of these statements are true?

  • Choose all that apply.

  • So pause this video, and see if you can work it out.

  • All right, now let's look through the choices.

  • So the first one says Katie threw the ball

  • from a height of five meters.

  • So let's see if that bears fruit

  • or (chuckles) see if that's true.

  • So if she threw it from a height of five meters,

  • that means that the y-intercept

  • would've been at five meters.

  • At time t equals zero,

  • we would've been at a height of five meters.

  • Clearly, that is not the y-intercept.

  • It looks like she threw it from a height

  • of maybe 1 1/2 or two meters.

  • So I'm assuming that Katie is not five meters tall.

  • So she wasn't on a ladder or anything.

  • She just threw it from her regular height.

  • And so we can rule out this first choice.

  • The second one says at its highest point,

  • the ball was about 31 meters above the ground.

  • Let's see if that is true.

  • So the highest point is right over here.

  • And yeah, that looks about 31 meters,

  • so I like that choice.

  • So I will select that one.

  • The ball was in the air for about 2 1/2 seconds.

  • So we can clearly see that that is not the case.

  • The ball was going up

  • for about 2 1/2 seconds, but then it was going down

  • for roughly another 2 1/2 seconds.

  • And so it was actually in the air for almost five seconds.

  • So I would rule this one out.

  • The ball reached its highest point in the air

  • about 2 1/2 seconds after Katie threw it.

  • So let's see, after Katie,

  • 2 1/2 seconds after Katie threw the ball,

  • it's right over there.

  • It looks like it reached its highest point

  • a little bit before that.

  • But they said about, so they're speaking in rough terms.

  • So I think that statement can be true.

  • It's about 2 1/2 seconds.

  • If they said exactly 2 1/2 seconds,

  • I wouldn't have selected it 'cause it seems like it happened

  • at like 2.45 seconds or something like that.

  • But there you go, those are the ones that seem true.

- [Instructor] Katie throws a ball in the air

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