(1) connects OA. From the meaning of the question, the radius of the small circle of the section is 4cm(2 points).

At Rt△OAO 1, O 1A=4, OO 1=3, we can know from the pythagorean theorem that AO=5, (4 points).

So, the surface area of ball O is: 4π? 25 = 100 π (cm2)。 (7 points)

(2) It is obtained from MN∥OA, where ∠OAC is the angle (or complementary angle) formed by non-planar straight line AC and MN. (9 points)

In Rt△ABC, AB=8, ∠ ABC = 30, then AC=4, (10).

Connect OC. At △OAC, OA=OC=5. According to the cosine theorem, COS ∠ OAC = AC2+OA2? OC22OA？ AC=42+52？ 522× 4× 5 = 25, (12 points)

Therefore, the angle between AC and MN is arccos 25. (14).