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WAEC 2022 Physics · Question 47

A small object of mass 50 g is released from a point A. Determine the velocity of the object when it reaches a…

Question

A small object of mass 50 g is released from a point A. Determine the velocity of the object when it reaches a point B, a vertical distance of 30m below A. [g = 10 ms−2^{-2}

  1. A.1.5 ms−1^{-1}
  2. B.6.0 m s−1^{-1}
  3. C.17.3 m s−1^{-1}
  4. D.24.5 m s−1^{-1}

Answer: D. 24.5 m s−1^{-1}

Explanation written with AI and checked against the answer key

Analyze the question: An object is released (so it starts from rest) and falls a vertical distance of 30 m. We need its speed at B. The mass (50 g) is not needed, because in free fall the speed does not depend on mass. Concept: Use conservation of energy (loss in potential energy = gain in kinetic energy), or equivalently the equation of motion v² = u² + 2gh. Solution: mgh = ½mv², so v² = 2gh (the mass cancels) With u = 0, g = 10 m/s² and h = 30 m: v² = 2 × 10 × 30 = 600 v = √600 ≈ 24.5 m/s Check against the options: √600 = 10√6 ≈ 10 × 2.449 = 24.5 m/s, which matches option D. (Option C, 17.3, is √300, which would come from forgetting the factor of 2.) Tip: In "released from rest" problems, the mass is usually a distractor. Go straight to v = √(2gh). Also remember that forgetting the "2" gives the common wrong option (here C).

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