Explain why scissors for cutting cloth may have blades longer than the handles, but shears for cutting metals have short blades and long handles.

A force of 5 kgf is required to cut a metal sheet. A pair of shears used for cutting the metal sheet has its blades 5 cm long, while its handles are 10 cm long. What effort is needed to cut the sheet ?

A pair of scissors has its blades 15 cm long, while its handles are 7*5cm long. What is its mechanical advantage ?

Explain why Alkenes have higher melting points than the alkanes with the same carbon skeleton.

Explain why angiosperms have been more successful than gymnosperms.

A man wants to cut three lengths from a single piece of board of length 91cm The second length is to be 3 cm longer than the shortest and the third length is to be twice as long as the shortest. What are the possible lengths of the shortest board if the third piece is to be at least 5cm longer than the second?

Antiseptic solution used to wash cuts and wounds in the body have surface tension lower than water. What is its advantages ?

Why do alkaline earth metals have higher melting points than group 1 elements ?

(a) Why alkaline earth metals are harder, have higer melting ponts and higher densities than the alkali metals? (b). Why the atoms of alkaline earth metals are smaller than the corresponding alkali metals? (c ). Why alkaline earth metals have high electrical and thermal conductivities? (d). What is black ash? (e). Why the variation in physical properties of alkaline earth elements is not as regular as in the case of alkali metals?

(i) Draw a neat labelled ray diagram of a compound microscope . Explain briefly its working . (ii) Why must both the objective and the eye-piece of a compound microscope have short focal lengths ?