A convex lens have focal length 30cm at what distance the object must be placed to form an image at 60cm?

Question

An object of mass m = 2 kg is lying on a rough inclined slope such that it is at rest. Find the magnitude of contact force acting on the object (in Newtons).

Assume
g=10
Coefficient of friction = .8
Angle of elevation = 30

Answer 1

Lens formula,
1/v - 1/u = 1/f
where,
v = image distance from lens
u = object distance from lens
f = focal length

here ,
f = 30 cm { for convex lens f is positive }
v = 60cm

1/60 - 1/u = 1/30 -> 1/60 - 1/30 = 1/u -> -1/60 = 1/u -> u = -60 cm
hence, object distance also 60cm but left side of convex lens . in which position of image is right side.

magnification = ( image distance )/(object distance ) = 60/(-60) = -1
it means height of image = height of object . but both lies just opposite sides of lens .