  We establish weighted Bernstein inequalities in $L^p$ space for the doubling
weight on the conic surface $\mathbb{V}_0^{d+1} = \{(x,t): \|x\| = t, x \in
\mathbb{R}^d, t\in [0,1]\}$ as well as on the solid cone bounded by the conic
surface and the hyperplane $t =1$, which becomes a triangle on the plane when
$d=1$. While the inequalities for the derivatives in the $t$ variable behave as
expected, there are inequalities for the derivatives in the $x$ variables that
are stronger than what one may have expected. As an example, on the triangle
$\{(x_1,x_2): x_1 \ge 0, \, x_2 \ge 0,\, x_1+x_2 \le 1\}$, the usual Bernstein
inequality for the derivative $\partial_1$ states that $\|\phi_1 \partial_1
f\|_{p,w} \le c n \|f\|_{p,w}$ with $\phi_1(x_1,x_2):= x_1(1-x_1-x_2)$, whereas
our new result gives $$\| (1-x_2)^{-1/2} \phi_1 \partial_1 f\|_{p,w} \le c n
\|f\|_{p,w}.$$
  The new inequality is stronger and points out a phenomenon unobserved
hitherto for polygonal domains.
