What is meant by focal length of lens

Which type of bond is found between the atoms of a molecule? a. metallic b. delocalized electron c. covalent d. ionic

Using a wheel and axle, a farmer is trying to lift a bucket of water from the bottom of a well. the larger wheel has a radius of 40 cm compared to the axle that has a radius of 10 cm. if a bucket of water is 50 n, then how much effort is required to raise it? 12.5 n 200 n 2 n 500 n

An object moves from position +34m to the position -15m in 15 seconds. what is the total displacement? what is the total velocity?