The second’s hand of a clock is 2.0 cm long. The average speed and modulus of average velocity of the tip of the seconds hand in 15 s are 

: Given that the tip of seconds hand started at A and reached B in 15s
r = 2.0s 
 

$\begin{array}{l}\text{ Distance }=\frac{2\mathrm{\pi r}}{4}=\frac{\mathrm{\pi r}}{2}\\ \text{ Displacement }=\mathrm{AB}\\ \text{ From }\mathrm{\Delta OAB}\\ {\mathrm{AB}}^2={\mathrm{OA}}^2+{\mathrm{OB}}^2\\ {\mathrm{AC}}^2=2^2+2^2\\ {\mathrm{AC}}^2=4+4=8\\ \mathrm{AC}=2\sqrt{2}\\ \text{ Average speed }\mathrm{v}=\frac{\mathrm{s}}{\mathrm{t}}=\frac{\mathrm{\pi }}{15}{\mathrm{cms}}^{-1}\\ \text{ Average velocity }\overrightarrow{\mathrm{v}}=\frac{\mathrm{s}}{\mathrm{t}}=\frac{2\sqrt{2}}{15}{\mathrm{cms}}^{-1}\end{array}$