WAEC Physics 2017 Objective — Question 9
Question 9 of 50 from the West African Examinations Council (WAEC) Physics 2017 Objective paper, with the correct answer and a full explanation.
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A body is projected horizontally from the top of a cliff 45m above the ground. If the body lands at a distance 30m from the foot of the cliff, calculate the speed of projection. [g = 10 ms⁻²]
- A. A. 10 ms⁻¹
- B. B. 15ms⁻¹
- C. C. 20ms⁻¹Correct
- D. D. 30ms⁻¹
Explanation
Given: Height of cliff, H=45m; Range, R=30m; speed of projection=ux (horizontal projection). From s=ut+½gt²: vertical motion gives s=H=½gt²; 45=½x10xt²; t²=(45x2)/10=9, t=3s. Horizontal resolution: s=uxt+½x0xt²; R=uxt; 30=uxx3; ux=10ms⁻¹. (Note: the official answer key states C, 20ms⁻¹; this may reflect a slightly different setup in the original figures.)
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