b) If this telescope is used to view a 100 m tall tower 3 km away, what is the height of the image of the tower formed by the objective lens?

Explanation

Angle subtended by tower 100 m tall at 3km
`alpha=(100)/(3xx1000)=(1)/(3)" radian"`
if his the height of image formed by the objective, then
`alpha=(h)/(f_(0))=(h)/(140)`
`therefore (h)/(140)=(1)/(30)`
`h=(140)/(30)=4.7cm`