Question

If you hold a 400 cm2 square plane mirror 41 cm from your eyes and can just see the full length of an 7.9 m flagpole behind you, how far are you from the pole? [Hint: A diagram is helpful.]

(Answer in METERS)

Answer 1

The square root of 400cm is 20cm, which gives you a 0.2m tall mirror. The flag pole appears 0.2m tall at 0.41m from you. It's really 7.9m. Total distance to the flagpole, visually, can be represented by this proportional equation:

0.41/0.3 = x/7.9, therefore:
x = (7.9)(0.41)/0.3 = 10.8m

But that's only the visual distance, from you to the mirror, and then back to the flagpole. Subtract the distance between you and the mirror twice to find your distance from the flagpole:

10.8m - 2(0.41m) = 9.98 m....Answer

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