WAEC Physics 2012 Objective — Question 9
Question 9 of 50 from the West African Examinations Council (WAEC) Physics 2012 Objective paper, with the correct answer and a full explanation.
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A stone of mass 300 g is released from rest from the top of a building of height 100 m. Determine the kinetic energy gained by the stone when it is a quarter way down from the point of release. [g = 10 ms⁻²]
- A. A. 750.0 J
- B. B. 225.0 J
- C. C. 75.0 JCorrect
- D. D. 22.5 J
Explanation
At the top, total energy = PE = mgh = 0.3x10x100 = 300 J. A quarter way down means it has fallen 25 m, so it is 75 m from the ground; PE at that height = 0.3x10x75 = 225 J. KE gained = total energy - PE = 300 - 225 = 75 J.
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