If $\frac{d^2y}{dx^2} = 0$,then

The least value of the natural number $n$ satisfying $C(n, 5) + C(n, 6) > C(n+1, 5)$ is

The equation of the tangent to the curve $y = b e^{-x/a}$ at the point where it crosses the $y$-axis is:

$100$ coplanar forces,each equal to $10 \, N$,act on a body. Each force makes an angle of $\pi / 50$ with the preceding force. What is the resultant of the forces? $(N)$

The height of the cone of maximum volume inscribed in a sphere of radius $R$ is

An iron rod of length $2 \, m$ and cross-sectional area of $50 \, mm^2$ is stretched by $0.5 \, mm$ when a mass of $250 \, kg$ is hung from its lower end. The Young's modulus of the iron rod is: