Question 976321
http://www.algebra.com/cgi-bin/display-illustration.mpl?tutor=anand429&illustration_name=2.jpg

Hints: Tangents from an external point to a circle/sphere are equal
Slant height of cone = sqrt(h^2+r^2) = 10

Rest. see. the figure in above link.

Volume = (4/3)pi(r^3)