Weekly Challenge 28: the Right Volume
If we suppose that the curve $y=f(x)$ is integrable then the volume
so created will be
$$
V = \int^1_0 \pi y^2 dx
$$
To get a feel for the sort of curve we might need, first consider
the special case $y=x$, which clearly passes through the two
points.
Then,
$$
V = \int^1_0 \pi x^2 = \pi\left[\frac{x^3}{3}\right]^1_0 =
\frac{\pi}{3}
$$
This is slightly larger than $1$, so we could consider a family of
curves which at beneath $y=x$ with enough flexibility to all us to
vary the final value of the volume. A simple choice is parabolas
$y=Ax(x-1)$ for some multiplicative constant. These
give
$$
V = \int^1_0 \pi Ax^2(x-1)^2dx
$$
Now that I see it, I'm not too keen on doing this integral, so I'm
going to consider instead $y=A\sqrt{|x(x-1)|}$
This gives a volume
$$
V = \int^1_0 \pi A x(1-x) dx = \pi
A\left[\frac{x^2}{2}-\frac{x^3}{3}\right]^1_0 = \pi A
\left[\frac{1}{2}-\frac{1}{3}\right] = \frac{\pi A}{6}
$$
Thus, a curve which has the required properties is
$$
y = \frac{6}{\pi}\sqrt{|x(x-1)|}
$$
There are, of course, others!