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Problem 8 - Entrance Test

A stone is thrown upward so that its height is h(t)=30t-5t² meters. When does it hit the ground (in seconds)?

Correct: D

Ground means h = 0 → 30t – 5t² = 0 → 5t(6 – t) = 0 → t = 0 or 6 → t = 6 s.