Advanced MathEasyEvaluating a quadratic model
Advanced Math practice question
A ball is thrown upward, and its height above the ground, in metres, t seconds after it is thrown is given by h(t) = −5t² + 20t.
What is the height of the ball, in metres, 3 seconds after it is thrown?
- A. 15Correct
- B. 105
- C. 45
- D. 60
Answer: A. 15
Substitute t = 3: h(3) = −5(3)² + 20(3) = −5(9) + 60 = −45 + 60 = 15 metres.
Why the other answers are wrong
- B. 105
- 105 is 5(9) + 60 — the negative sign on the t² term was dropped. The first term is −45.
- C. 45
- 45 is −5(3) + 20(3), using t instead of t². The first term squares t: (3)² = 9.
- D. 60
- 60 is just 20(3). The −5t² term must be included: 60 − 45 = 15.
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