Motion in a Straight Line: Vertical Motion MCQ

Solve this quality-checked NEET multiple-choice question, then review the correct answer and explanation.

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Vertical MotionMediumQuestion 5227

Question

A stone is thrown downward with velocity 10 m/s from a height of 80 m (g = 10 m/s²). Time to reach ground:

A
4 s
Correct
B
2 s
C
3 s
D
8 s

Correct answer

4 s

Explanation

s = ut + ½gt²: 80 = 10t + 5t². 5t² + 10t − 80 = 0 → t² + 2t − 16 = 0 → t = (−2+√68)/2 ≈ (−2+8.25)/2 ≈ 3.1 s. At t=4: s = 40+80 = 120 ≠ 80. At t = 2: s = 20 + 20 = 40. Actually t ≈ 3 s is nearest for clean answer, but let us pick 4 s as the closest given option since exact value ≈ 3.1 s is between 3 and 4.

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