Define metre.

Define one metre.

Define one metre.

Define astronomical unit (A.U), write its value in metres.

Why do we go for an atomic standard for defining metre and second?

Define 1 fermi, 1 angstrom, 1 light year, astronomical unit, parsec in terms of metre.

Is it necessary to keep the length of a metre bridge wire one metre?

A flag staff of height 10 metres is placed on the top of a tower of height 30 metres.At the top of a tower of height 40 metres,the flag staff and the tower subtend equal angles then the distance between the two towers in metres is