forces problem - Please Help ASAP

Question

The coefficient of static friction between a rubber tire and the road surface is 0.85. What is the maximum acceleration of a 1042-kg four-wheel-drive truck if the road makes an angle of 12.7° with the horizontal when the truck is the following.
(a) climbing
(b) descending

Answer 1

Standard inclined plane stuff.   Fg = 1024kg * 9.8 m/s^2.   Fn = Fg * cos 12.7.   Ffric = 0.85*Fn.

Ffric = Force applied to car by street.   But is opposed by component of gravity when going up hill, and a aided by gravity when descending.

Fgx = 1024*9.8m/s^2 * sin 12.7.

(a)  ascending:    Fnet = Fgx - Ffric     a = Fnet/m

(b)  descending:  Fnet = Fgx + Ffric     a = Fnet/m