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NEET Physics QUESTION #7307
Question 1

A stone falls freely from rest. The distance covered in the last second of motion equals the distance covered in the first 3 seconds. How long does the stone take to reach the ground?

  • 5 s✔️
  • 12 s
  • 15 s
  • 3 s
Correct Answer Explanation

Distance in first 3 s: $s_3 = \dfrac{1}{2}(10)(3)^2 = 45\text{ m}$

Distance in last 1 s of total time $T$ (using $s_n = u + \dfrac{a}{2}(2n-1)$ with $u=0$):

$s_{\text{last}} = \dfrac{g}{2}(2T-1) = 5(2T-1)$

Setting equal: $5(2T-1) = 45 \Rightarrow 2T-1 = 9 \Rightarrow T = \mathbf{5\text{ s}}$