The sine component of gravitational force from a mass element da at a distance 3R + dr and its counterpart at opposite end cancel each other. Thus, the total gravitational force at point p is the mass density σ, which is given as σ =
M
2πR2(16−9)
=
M
14πR2
Now, V = -
4R
∫
3R
Gσ2πrdr
√r2+16R2
= −G2π
4R
∫
3R
rdr
√r2+16R2
V = Gσ2π|√r2+16R2|3R4R = Gσ2πR(4√2−5) Substituting the value of σ, we get V =