Advanced MathMediumTime when a projectile returns to its launch height
Advanced Math practice question
The height, in metres, of a ball t seconds after it is thrown is h(t) = −5t² + 10t + 15. For what value of t > 0 is the ball back at its launch height?
Answer: 2
The launch height is h(0) = 15. Set −5t² + 10t + 15 = 15: −5t² + 10t = 0 → −5t(t − 2) = 0 → t = 2.
Common wrong answers
- If you answered 1
- 1 is when the ball is at its highest point.
- If you answered 3
- 3 is when the ball hits the ground (h = 0).
- If you answered 15
- 15 is the launch height, not a time.
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