`a) 1/4 `vòng đầu

`s_1=1/4.C=1/4.\pi.2r={\pir}/2={3,14.3}/2=4,71(cm)=0,0471(m)` 

`v_1={s_1}/{t_1}={0,0471}/2=0,02355`$(m/s)$

`d_1=\sqrt{r^2+r^2}=\sqrt{3^2+3^2}=3\sqrt2(cm)=0,03.\sqrt2(m)` 

`V_1=d_1/t_1={0,03.\sqrt2}/2=0,015\sqrt2`$(m/s)$

`b)` nửa vòng tiếp theo

`s_2=1/2.C=1/2.\pi.2r=\pir=3,14.3=9,42(cm)=0,0942(m)` 

`v_2={s_2}/{t_2}={0,0942}/3=0,0314`$(m/s)$

`d_2=2r=2.3=6(cm)=0,06(m)`

`V_2=d_2/t_2={0,06}/3=0,02`$(m/s)$

`c)` đoạn còn lại

`s_3=s_1=1/4.C=1/4.\pi.2r={\pir}/2={3,14.3}/2=4,71(cm)=0,0471(m)` 

`v_3={s_3}/{t_3}={0,0471}/{6-2-3}=0,0471`$(m/s)$

`d_3=\sqrt{r^2+r^2}=\sqrt{3^2+3^2}=3\sqrt2(cm)=0,03.\sqrt2(m)`

`V_3=d_3/t_3={0,03.\sqrt2}/{6-2-3}=0,03\sqrt2`$(m/s)$

`d)` cả vòng tròn

`s_4=C=\pi.2r=3,14.3.2=18,84(cm)=0,1884(m)`

`v_4=s_4/t_4={0,1884}/6=0,0314`$(m/s)$

`d_4=0(m)`

`V_4=d_4/t_4=0/6=0`$(m/s)$