A runner starts from O and goes to O following path OQRO in 1 h. What is net displacement and average speed? 

$\because$  Runner starts from O and goes to O following the path OQRO, so net displacement is zero.

$\because$ Average speed $=\frac{\text{ Total distance }}{\text{ Total time }}=\frac{OQ+QR+RO}{\text{ Total time }}$

                               $=\frac{1 \mathrm{km}+\left(2\pi r\right)(1/4)+1 \mathrm{km}}{1 \mathrm{h}}$

                                $=2+\frac{\pi }{2}=3.57{\mathrm{kmh}}^{-1}$