A 12 cm vertical stick casts an 8 cm shadow at the same time a tower casts a 40 m shadow. Assuming the same sun elevation (similar triangles), find the height of the tower (in metres).

Difficulty: Easy

Correct Answer: 60 m

Explanation:


Introduction / Context:
When two vertical objects cast shadows simultaneously, the triangles formed by height and shadow length are similar (same sun elevation). Therefore, height is proportional to shadow length; we scale from the stick to the tower.


Given Data / Assumptions:

  • Stick height = 12 cm; its shadow = 8 cm.
  • Tower shadow = 40 m.
  • Both are vertical; ground is level; same sunlight angle (similarity).


Concept / Approach:

  • For similar triangles: height/shadow is constant.
  • Convert units consistently (use metres).


Step-by-Step Solution:

Convert: 12 cm = 0.12 m, 8 cm = 0.08 mHeight ratio = 0.12 / 0.08 = 3/2 = 1.5Tower height H = 1.5 * (tower shadow) = 1.5 * 40 = 60 m


Verification / Alternative check:
Proportion in centimetres also works: 12/8 = H_cm / 4000 ⇒ H_cm = 6000 cm ⇒ 60 m.


Why Other Options Are Wrong:

  • 600 m and 160 m: Incorrect scaling or unit mistakes.
  • 52 m: Random deviation; not in 3:2 ratio.
  • None of these: Not applicable; 60 m is exact.


Common Pitfalls:

  • Mismatched units (cm with m) causing wrong scale.
  • Assuming non-parallel sun rays; here standard assumption holds.


Final Answer:
60 m

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