Skier follows a curve

Since the speed is constant there is no tangential acceleration the only acceleration is in radial direction which can be given by

$a=\frac {v^{2}}{r}$

where r can be calculated by the formula

$r=\frac {[1+(\frac{dy}{dx})^{2}]^\frac {3}{2}}{\frac {d^{2}y}{dx^{2}}}$

$y=\frac {x^{2}}{20}$

$\frac {dy}{dx}=\frac {2x}{20}=\frac {x}{10}$

$\frac {d^{2}y}{dx^{2}}= \frac {d}{dx}(\frac {dy}{dx})=\frac {d}{dx}(\frac {x}{10})=\frac{1}{10}$

Putting in the values we get

$\frac {dy}{dx}=\frac {10}{10}=1$

$r=\frac {[1+(\frac{dy}{dx})^{2}]^\frac {3}{2}}{\frac {d^{2}y}{dx^{2}}}=20\sqrt {2}$

$a=\frac {9\sqrt {2}}{10}$

$Ans.is \boxed{21}$