# during a daytime football game you notice that a player's reflective helmet forms an image of the sun 4 cm behind the surface of the helmet. what is the radius of curvature of the helmet, assuming...

during a daytime football game you notice that a player's reflective helmet forms an image of the sun 4 cm behind the surface of the helmet. what is the radius of curvature of the helmet, assuming it to be roughly spherical

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### 1 Answer

You need to evaluate the radius of curvature of helmet whose behavior is similar to behavior of convex spherical mirror, using the following equation, such that:

`R = 2*f`

f represents the focal length

The problem provides the information that the image forms behind the surface of helmet, hence the focal distance is negative, such that:

`R = 2*(-4) => R = -8 cm`

**Hence, evaluating the radius of curvature of helmet, under the given conditions, yields `R = -8cm.` **