v₁=0 m/s
v₂=60 km/h
v₃=0 m/s
t₁=1 min = 60 s
t₂=20 min
t₃=30 s
[tex]60 \ \frac{km}{h}=60\frac{1000 \ [m]}{3600 \ [s]}=16,(6) \ \frac{m}{s}[/tex]
a)
[tex]a_1=\frac{\Delta v_1}{t_1}=\frac{v_2-v_1}{t_1} =\frac{16,(6) \ \frac{m}{s}}{60 \ s}=0,2(7) \ \frac{m}{s^2}[/tex]
[tex]a_2=\frac{\Delta v_2}{t_3}=\frac{v_3-v_2}{t_3} =\frac{-16,(6) \ \frac{m}{s}}{30 \ s}=-0,(5) \ \frac{m}{s^2}[/tex]
b)
[tex]S_1=\frac{a_1t_1^2}{2}=\frac{16,(6) \ \frac{m}{s^2} *[60 \ s]^2}{2}=499,(9) \ m\\ \\S_2=v_2*t=16,(6) \ \frac{m}{s} *1200 \ s=19999,(9) \ m\\ \\S_3=v_2*t_3+\frac{a_2t_3^2}{2}=16,(6) \ \frac{m}{s}*30 \ s+ \frac{-0,(5) \ \frac{m}{s^2}*[30 \ s]^2}{2}=250 \ m[/tex]
[tex]v_{\'sr}=\frac{S_1+S_2+S_3}{t_1+t_2+t_3}=\frac{499,(9)+19999,(9)+250 \ m}{60+1200+30 \ s}\approx16,085 \ \frac{m}{s}[/tex]
