Question

Starting from rest, a disk rotates about its central axis with constant angular acceleration. In 4.0 s, it has rotated 30 rad.

Assuming that the acceleration does not change, through what additional angle will the disk turn during the next 7.0 s?

I calculated the acceleration to be 3.75 rad/s^2

Answer 1

Displacement=1/2 alpha*t^2
alpha=2*30/16

2)
d=wi*t+1/2 alpha(7^2)
where wi=alpha*4
d=alpha*4+1/2 alpha*49
and solve for additional displacemetn d.

Answer 2

so, (3.75)(4) + (.5)(3.75)(49) or 106.875?

or just the second part to find the additional angle?

(.5)(3.75)(49) = 91.875 but it is incorrect, what am I missing?