Motion in a Straight Line

A new unit of length is chosen such that the speed of light in vacuum is unity. What is the
distance between the sun and the earth in terms of the new unit if light takes 8 min and
20 s to cover this distance. [NCERT]

Which of the following is the most precise device for measuring length :
(?) a vernier callipers with 20 divisions on the sliding scale.
(b) a screw gauge of pitch 1 mm and 100 divisions on the circular scale.
(c) an optical instrument that can measure length to within a wavelength of light ?
[NCERT]

What is a unit ?

Distinguish between fundamental and derived units.

Explain this statement clearly:
"To call a dimensional quantity large' or 'small' is meaningless without specifying a standard
for comparison". In view of this, reframe the following statements wherever necessary :
(a) Atoms are very small objects.
(b) A jet plane moves with great speed.
(c) The mass of jupiter is very large.
(d) The air inside this room contains a large number of molecules.
(e) A proton is much more massive than an electron.
(f) The speed of sound is much smaller than the speed of light. [NCERT]