A Numerical from Combination of thin lenses in contact

Two thin lenses of focal lengths f1=20cm and f2=60cm are placed in contact. find the focal length f3 of the combined lenses. find also the focal length f of a third lens placed in contact with these two that would result in overall focal length f11=-40cm. (Asked Young) Incoming search terms:class 9 science sample paper for [...]

A Numerical Problem from Mechanics

A rock explodes and is split into three pieces. two of them moves in direction of perpendicular to each other. One piece of mass 1kg moves with velocity of 5m/s and second piece of mass 2kg moves with velocity of 13m/s. find mass of third piece. (Tayade Kishore S asked)   Incoming search terms:numerical problems [...]