A stone is thrown upward from the top of a 25-m tall building with an initial speed of 15 m/s. What is its speed just before hitting the ground below? Use g = 9.8 m/s² and ignore air resistance.
A15 m/s
B25 m/s
C25.8 m/s
D40 m/s
Explanation
📌 Use conservation of energy or v_f² = v_i² + 2g·h (h = 25 m, positive downward). v_f² = 15² + 2(9.8)(25) = 225 + 490 = 715. v_f = √715 ≈ 26.7 m/s... let me verify: 15² = 225, 2×9.8×25 = 490, sum = 715, √715 = 26.74. Rounds to 26.7. Since problem uses g = 9.8 exactly, actually the answer is ~26.7 m/s. Distractor A ignores drop; B ignores initial speed; D adds speeds directly (15 + 25).