Answer
(a) $0.49$
(b) no change to the angle ($26^{\circ}$)
Work Step by Step
(a) We can find the coefficient of static friction as
$\Sigma F_y=N-mgcos\theta=0$
$\implies N=mgcos\theta$
Now the horizontal component of force is
$F_x=\mu_sN-mgsin\theta=ma_x=0$
$\implies \mu_s(mgcos\theta)-mgsin\theta=0$
This simplifies to:
$\mu_s=tan\theta$
$\implies \mu_s=tan26^{\circ}$
$\mu_s=0.49$
(b) We know that the angle does not depend on the mass. Thus, if mass is doubled, the angle remains the same.
