Question

is anyone good at physics?

Answer 1

theres another section for physics

Answer 2

my scecialty! haha

Answer 3

nobody is helping me in that section

Answer 4

its applied math

Answer 5

what is your question i can help you

Answer 6

the question is

a person's face is 30 cm in front of a concave mirror. if the image is an erect image 1.5 times as large as the object, what is the mirror's focal length?

Answer 7

ok let me worth this out

Answer 8

the answer is 90 cm :)

Answer 9

can you tell me how you got that?

Answer 10

yes this is going to be very hard to explain but let me try haha

Answer 11

im only 16 but im very good in physics haha

Answer 12

lolz im 16 and very bad. so how did you find 90?

Answer 13

ok lets see

Answer 14

do you know about concave and convex like are you familiar

Answer 15

i know that convex mirror is like (
and concave mirror is like )

Answer 16

ds can you exxplain it ?

Answer 17

i'm pretty sure yankeefan just googled it, otherwise it wouldn't be that difficult to explain.

Answer 18

Use the mirror equation:

1/di + 1/do = 1/f

Answer 19

i didn't google it haha im not an idiot

Answer 20

yes. so that is 1/f= 1/30 +1/45

Answer 21

now what?

Answer 22

solve for f, which is the focal length

Answer 23

right. so this is what i did.

1. found the common denominator (90)
so 1/30 +1/45 -> 3/90 + 2/90

2. thats 5/90

Answer 24

which i think is 18

Answer 25

yeah it is.

Answer 26

\[\frac{1}{f}=\frac{1}{d_{0}}+\frac{1}{d_{i}}\]f = focal length
d0 = distance from mirror to object
di = distance from mirror to image
\[m=\frac{-d_{i}}{d{0}}\]m = magnification\[\frac{3}{2}=\frac{-d_{i}}{30}\]\[-45=d_{i}\]\[\frac{1}{f}=\frac{1}{30}+\frac{1}{-45}\]\[f=90\]I Googled it.

Intuition > Memory

Answer 27

The formulas, that is.