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Q26
(CISF/2026)
Science & Technology › Basic Science (Physics, Chemistry, Biology)
A person of height 6 feet is standing at a distance of 12 feet from the foot of a lamp post of height 30 feet. What is the length of his shadow formed on the ground ?
Result
Your answer:
—
·
Correct:
A
Explanation
This problem is solved using the geometric principle of similar triangles, which is a core concept in optics (Physics) regarding shadow formation. Let the lamp post be represented by a vertical line of 30 ft and the person by a vertical line of 6 ft.
- Let s be the length of the shadow.
- The distance from the lamp post to the person is 12 ft.
- The total distance from the lamp post to the tip of the shadow is 12 + s.
Because the triangles formed by the lamp post and the person with the tip of the shadow are similar, the ratio of their heights must equal the ratio of their bases:
Height of Lamp / Total Base = Height of Person / Shadow Base
30 / (12 + s) = 6 / s
5 = (12 + s) / s
5s = 12 + s
4s = 12
s = 3 feet.
Therefore, the length of the shadow is 3 feet.
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