∫P = Wt = Fst = Fv，
∴F=Pv，
∵ P2 > P 1, the speed is constant.
∴ When the car is driving in BC section, the traction is great.
(2) Let BC be L in length and H in height, and we can get from the relation of work:
WF=Gh+fL
P2(T2-t 1)= G(H2-h 1)+fL
P2(T2-TL)= G(H2-h 1)+Fv(T2-TL)
f=P2(t2？ t 1)？ G(h2？ h 1)V(t2？ t 1)？ (noun)
Answer: (1) When the car is driving in BC section, the traction is large;
(2) The expression of the total resistance when the car runs along the BC section of the slope: f = p2 (t2? t 1)？ G(h2？ h 1)V(t2？ t 1)？ (N)。