it's a question about physics

2008-10-26 7:19 am

in a dancing room, dancer P stands 1 m in front of a plane mirror. He is equidistand from dancers Q and S who are standing 2 m in front ot the mirror. The distance between Q and S is 3 m. Find the minimum width of the mirror for dancer P to see both dancers Q and S

回答 (1)

天同

2008-10-26 8:41 am

✔ 最佳答案

Dancers Q and S are standing 2 m in front of the mirror, thus, their images formed by the mirror are at a distance of 2 m behind the mirror.

After locating the images of Q and S, draw a ray diagram showing how the light rays from the images of Q and S reach dancer P.

There will then be two isosceles similar triangles, with P as the comon apex and images of Q and S forming the base of one triangle, and the mirror forming the base of another triangle.

Therefore, w/1 = Q'S'/3
where w is the width of the mirror, and Q'S' is the separation between images of Q and S, which is 3 m

Hence, w = 3/3 m = 1 m

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