An older camera has a lens with a focal length of 60mm and uses 34-mm-wide film to record its images. using this camera, a photographer takes a picture of the golden gate bridge that completely spans the width of the film. now he wants to take a picture of the bridge using his digital camera with its 14-mm-wide ccd detector. what focal length should this camera's lens have for the image of the bridge to cover the entire detector?

24.71 mm

Explanation:

Distance is proportional to focal length, so

d∝f

which means

Magnification of first lens

                   and

Similarly, magnification of second lens

                   and

From the above equations we get

                   and

which means,

and

So, we get

∴ Focal length should this camera's lens is 24.71 mm

one person pulls 90n one way and the other has 100n pulling the other way.

so the net force = 90 - 100 = -10n,

or the ans can be 10n if the picture shows -90n and 100n instead.