Rotational (angular) acceleration:
α = 7 rad/s²
Time evolution:
i) angular velicty: ω(t) = αt
(Same approach as the motion of uniform acceleration)
with rest condition: ω(0) = 0
ii) Rotation: θ(t) = ½αt²
with setting initial angle : θ(0) = 0
We need to find t for θ(t) = 14
½αt² = (7/2)t² = 14
→ t² = 28 ÷ 7 = 4
∴ t = 2
It takes 2 seconds for 14 rotations.
The diameter is not important information for this problem.