The image of a needle placed 45cm from a lens is formed on a screen placed 90cm on the other side of lens.Find displacement of image if object is moved 5cm away from lens

first of all we will  calculate focal lenght from lens formula 1/v - 1/u = 1/f

 put u = -45

1/90 + 1/45 = 1/f 

it gives f = 30

Now again use lens formula and obtain image distance for u = - 50

you will get v = 75

Displacement = 90 - 75 = 15 cm

thanks

keep posting