52278612
A tennis player hits a ball straight upward. Its height \(h\), in meters, after \(t\) seconds is modeled by \(h(t) = -4.9t^2 + 12t + 1.5\). Use the first and second derivatives to determine when the ball reaches its highest point and the height of that point.
Hints
- What condition does the first derivative satisfy at the highest point?
- How does the second derivative confirm that the point is a maximum?
- What does the value of \(h(t)\) represent?
Solution
1. Differentiate: \(h'(t) = -9.8t + 12\) and \(h''(t) = -9.8\).
2. Solve \(h'(t) = 0\): \(-9.8t + 12 = 0\), so \(t = \frac{60}{49} \approx 1.224\,\text{s}\).
3. Since \(h''(t) = -9.8 < 0\), the critical time gives a maximum.
4. Evaluate the height: \(h(\frac{60}{49}) = \frac{867}{98} \approx 8.85\,\text{m}\).
Answer
The ball reaches its highest point after approximately \(1.22\,\text{s}\), at a height of approximately \(8.85\,\text{m}\).
