Answer
$8\pi$
Work Step by Step
First, plug in 0 for y in $y = \sqrt x-1$
Second, solve for $x$ to get the intersection points which would tell your $a$ and $b$
Third, use the disk method $v=A(x)dx$
$A(x)$ being $A(x)=\int\pi*r^{2}$
Fourth, plug in the radius $\sqrt x-1$ and find the integral
then solve.