Why should we use fossil fuels only when absolutely necessary ?
Why should we use only mirrors for plane mirrors for reflection ,why can't we use a glass or a book for plane surface? Even book is a regular surface.
Give reasons why :
(a) Travelling bags have wheels.
(b) Iron pipes are fitted on an inclined plane for pushing up heavy loads.
(c) We should take care of machines.
(d) We should use a pulley to draw water from a well.
