A wall clock has a 5 cm long minutes hand. The average velocity of the tip of the hand reaching 6:00 hour to 18:30 hour is 

Given that a minutes hand has its tip started at A
At 6 hour reaches B at 18:30 hour
Displacement d = AB = 2r
r = 5cm
t = 6 to 18:30 hr
t = 12 hr 30min
t = 45000 s
$\begin{array}{l}\mathrm{v}=\frac{\mathrm{d}}{\mathrm{v}}=\frac{5\mathrm{cm}+5\mathrm{cm}}{45000\mathrm{s}}\\ \because [\mathrm{d}=2\mathrm{r}]\\ [2\times 5=10\mathrm{cm}]\\ \mathrm{v}=\frac{10}{45000}=2.2\times {10}^{-4}{\mathrm{cms}}^{-1}\\ 2.2\times {10}^{-4}{\mathrm{cms}}^{-1}\end{array}$