$A$ huge circular arc of length $4.4 \; ly$ subtends an angle of $4''$ (arcseconds) at the centre of the circle. How long would it take for a body to complete $4$ revolutions if its speed is $8 \; AU/s$?
Given: $1 \; ly = 9.46 \times 10^{15} \; m$,$1 \; AU = 1.5 \times 10^{11} \; m$.

It is a well-known fact that during a total solar eclipse,the disk of the Moon almost completely covers the disk of the Sun. From this fact and the information given below,determine the approximate diameter of the Moon.
Distance of the Moon from the Earth $= 3.84 \times 10^{8} \; m$
Distance of the Sun from the Earth $= 1.496 \times 10^{11} \; m$
Diameter of the Sun $= 1.39 \times 10^{9} \; m$

Given below are densities of some solids and liquids. Give rough estimates of the size of their atoms.

Substance	Atomic Mass $(u)$	Density $(10^3\,kg\,m^{-3})$
Carbon (diamond)	$12.01$	$2.22$
Gold	$197.00$	$19.32$
Nitrogen (liquid)	$14.01$	$1.00$
Lithium	$6.94$	$0.53$
Fluorine (liquid)	$19.00$	$1.14$

Explain accuracy and precision in measurement.

Which of the following is the most precise device for measuring length?

When the planet Jupiter is at a distance of $824.7 \; \text{million km}$ from the Earth, its angular diameter is measured to be $35.72''$ of arc. Calculate the diameter of Jupiter.