【单选题】A uniform ball of mass M = 6.00kg and radius R rolls smoothly from rest down a ramp (斜坡) at angle θ = 30.0 o . The ball descends a vertical height h = 1.20m to reach the bottom of the ramp. What is it...
A.
v COM = 5.10m/s, f s = 8.40N, upward along the ramp
B.
v COM = 4.10m/s, f s = 10.40N, upward along the ramp
C.
v COM = 4.10m/s, f s = 8.40N, downward along the ramp
D.
v COM = 4.10m/s, f s = 8.40N, upward along the ramp