試題詳解

4. A circular track of radius 1000 meters is banked at 30 degrees without any friction. What is required speed for a car to keep running on the circular track?
(A) about 30 m/s
(B) about 45 m/s
(C) about 55 m/s
(D) about 65 m/s
(E) about 75 m/s