According to v=st, the first half is s 1=v 1t,
In the second half of the time, through the displacement of s2=v2t,
Total distance s=s 1+s2=v 1t+v2t,
The average speed is v = st = v1t+v2tt = v1+v22;
(2) If the total distance is s, the first half distance and the second half distance are 12s.
From v=st:
Time spent in the first half of the journey:
t 1 = 12sv 1 = s2v 1，
Time spent in the second half of the journey:
t2= 12sv2=s2v2，
Full cycle driving time:
t=t 1+t2=s2v 1+s2v2，
Average speed of the whole journey:
v = ST = ss2v 1+S2 v2 = 2v 1v2v 1+v2 = 2×3m/s×2m/s3m/s+2m/s = 2.4m/s。
A:
(1) The derivation process is the same as above;
(2) The average speed is 2.4m/s. 。