Answer
The proof is below.
Work Step by Step
We call the center of wheel the axis of rotation. Thus, we find:
$mgcos\theta=(M+m)gsin\theta$
$mcos\theta-msin\theta=Msin\theta$
$m=\frac{Msin\theta}{cos\theta-sin\theta}$
$m>\frac{Msin\theta}{1-sin\theta}$
