Solution:
SOLUTION :
Here direction of Motion will be reversed when force F = 0 or 20 t – 5t2 = 0 or t = 4sec.
If α is angular acceleration then torque τ = Iα = F.r
OR 10 × α = (20 t – 5t2 ) × 2
OR α = 4t - t2
2π = 44/7 rad = 1 rotation
Therefore 64/3 rad = 3.4 rotation option "a" is correct
