A thin uniform annular disc of mass M has outer radius 4 R and inner radius 3 R. the work required to take unit mass from point P on its axis to infinity is:

Q: A thin uniform annular disc of mass M has outer radius 4 R and inner radius 3 R. the work required to take unit mass from point P on its axis to infinity is:

(a) $\frac{2 G M}{7R}(4\sqrt{2}-5)$

(b) $- \frac{2 G M}{7R}(4\sqrt{2}-5)$

(c) $\frac{ G M}{4 R}$

(d) $\frac{2 G M}{5 R}(\sqrt{2}-5)$