A lens of focal length 25.0 cm forms an image 37.5 cm from the lens. What was the object distance?

it can be 15 or 75

Explanation:

using this equation

f = focal length

so = object distance

si = image distance

since we do not now what lens used, I assume from the problem the lens are positive (convex) but I don't know the image position because lens have two side.

1. the positif lens with negative image distance (it means object and image are in the same side of lens)

1/25 = 1/so - 1/37.5

1/so = 1/25 + 1/37.5 = 1/15

so = 15 cm in front of the lens (same side with the image)

2. the positif lens with positive image distance (it means object and image are not in the same side of lens)

1/25 = 1/so + 1/37.5

1/so = 1/25 - 1/37.5 = 1/75

so = 75 cm in front of the lens (not in the same side with the image)

no sign of dia of fuel cell

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.