¯v=S/t=S/(t_1+t_2 )=S/(S/(2v_1 )+S/(2v_2 ))=2*v_1*v_2/(v_2+v_1 )
v_2=¯v*v_1/(2*v_1-¯v)=60*65/(120-65)=3900/55=71м/с
¯v=S/t=S/(t_1+t_2 )=S/(S/(2v_1 )+S/(2v_2 ))=2*v_1*v_2/(v_2+v_1 )
v_2=¯v*v_1/(2*v_1-¯v)=60*65/(120-65)=3900/55=71м/с