Advanced MathVery hardTime in the air from vertex form
Advanced Math practice question
The height h, in metres, of a ball t seconds after it is kicked from the ground is modelled by h(t) = −5(t − 2)² + 20. For how many seconds is the ball above the ground?
Answer: 4
Set h = 0: (t − 2)² = 4, so t = 0 (the kick) or t = 4 (the landing). The ball is in the air for 4 seconds.
Common wrong answers
- If you answered 2
- 2 is the time to the highest point, half the flight.
- If you answered 8
- 8 doubles the flight time by adding the two roots' distances the wrong way.
- If you answered 20
- 20 is the maximum height, not a time.
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