# physics

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1)A 5.0 cm real object is placed at a distance of 30.0 cm from a concave mirror of focal length 10.0 cm. Find the location of the image.

(30)(10)/5.0
15

or (30)(5.0)/10
60

I don't know which one

2)What must be the minimum height of a plane mirror so that a boy of height 162 cm can view himself from head to toe?

162 cm

3)A 5.0 cm real object is placed at a distance of 5.0 cm from a concave mirror of focal length 10 cm. Find the size of the image.

20 cm

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3)(10)(5.0)/5.0-10
answer: 10 cm (I get -10 from the math but that's not one of the choices)

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3) I skipped a step but 10 is still the answer.

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1/do + 1/di = 1/f = 1/10
1/30 + 1/di = 1/10
1/di = 2/30
One of your answers is correct, but you used the wrong formula to get it.

di = 15 cm is the distance to the image. It makes no difference what the object height is.

2) wrong

3) wrong. You are just taking wild guesses. That won't do.

1/5 + 1/di = 1/10
1/di = 1/10 - 2/10 = -1/10
di = -10
Magnification = |di/do| = ?
Image size = (object size) * (magnification)= ?

• physics-it may look like it but im not -

it may look like it but im not

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So I was right originally on 3, with 20 cm. For 2, 162/2 = 81 cm

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mag = di/do
mag = -10/5.0
mag = 2

im size = o-size * mag
im size = 5.0 * 2
im size = 10

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15