Help with physics homework problem

[Aikenfan]

Homework Statement

If anyone can help me, i would really appreciate it! thanks

Homework Equations

The Attempt at a Solution

 

[Aikenfan]

would i do:
15.5^-1 - 2.96^-1
Ans^-1
-3.658

 

[hage567]

i does not equal 2.96. You've just dropped a variable, you can't do that. If M = -i/o, then i = -M*o, right? Remember there should be a negative sign in the magnification equation when you are dealing with object and image distances. Now you know what i is in terms of o, so using the lens equation and a little algebra you can solve for o.

 

[Aikenfan]

1/15.5 = 1/2.96*o + 1/o

Im sorry i believe i typed that wrong the first time, i forgot the "o" after 2.96
do i find the common denominator, i am not sure what to do

 

[hage567]

1/15.5 = 1/2.96*o + 1/o

Im sorry i believe i typed that wrong the first time, i forgot the "o" after 2.96
do i find the common denominator, i am not sure what to do

You are still forgetting the negative sign in the M equation. To find "o", you can just take it out so you will have (1/o)*(1-(1/2.96)) on the right side of the lens equation. You can then cross multiply to solve for "o".

Once you get your answer for "o", find "i". You can put them both back into the lens equation and check if they are right, since you were given f.

 

[Aikenfan]

so o is equal to 0.663?

 

[hage567]

No, you're not quite finished yet. You should be at (1/15.5) = (1/o)*(0.663). Now you must isolate "o" and solve for it. You can just cross multiply, since what you have is the same as (1/15.5)=(0.663/o). Do you see what I mean?

 

[Aikenfan]

when i cross multiply, i get:
15.5 (0.663)
=
10.2765
does that look correct?

 

[hage567]

Yes, I think that looks OK.