physics
posted by Jon on .
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

3)(10)(5.0)/5.010
answer: 10 cm (I get 10 from the math but that's not one of the choices) 
3) I skipped a step but 10 is still the answer.

1) Start with the lens or mirror equation:
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)= ? 
it may look like it but im not

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

mag = di/do
mag = 10/5.0
mag = 2
im size = osize * mag
im size = 5.0 * 2
im size = 10 
15