Question:medium

A stone is dropped from a height of 45 m. What is the time taken for the stone to reach the ground?

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This is a case of free fall starting from rest, so the initial velocity is zero and acceleration equals g (take $g = 10\,m/s^2$ unless a different value is given). You can either apply $h = \frac{1}{2}gt^2$ directly, or first find the final velocity using $v^2 = 2gh$ and then use the average velocity to reach the time, both routes work equally well.
Updated On: Aug 17, 2026
  • 3 s
  • 5 s
  • 6 s
  • 9 s
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The Correct Option is A

Solution and Explanation

The calculation determines the time for an object to fall from a given height under gravity. Using the free fall equation without initial velocity, h = 1⁄2 gt2, where:
  • h represents height (45 m)
  • g represents the acceleration due to gravity (9.8 m/s2)
  • t is the time in seconds
Substituting the given values: 45 m = 1⁄2 (9.8 m/s2) t2. Solving for t2: 45 m = 4.9t2, which leads to t2 = 45 m⁄4.9 m/s2, resulting in t2 = 9.18. Therefore, t ≈ √9.18 ≈ 3.03 s.
Rounded to the nearest second, t ≈ 3 s.
The time for the object to reach the ground is approximately 3 seconds. The correct answer is 3 s.
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