A solid consists of a cone on top of a cylinder with a radius equal to that of the cone. The height of the cone is 12 12 and the height of the cylinder is 28 28. If the volume of the solid is 36 pi36π, what is the area of the base of the cylinder?

1 Answer
Apr 20, 2018

color(blue)((9pi)/8)9π8

Explanation:

Volume of a cone is given by:

V=1/3pir^2hV=13πr2h

Volume of a cylinder is given by:

V=pir^2hV=πr2h

We know height of cone and cylinder:

V=1/3pir^2(12)V=13πr2(12)

V=pir^2(28)V=πr2(28)

The sum of these two volumes is 36pi36π given:

:.

pir^2(28)+1/3pir^2(12)=36pi

28pir^2+4pir^2=36pi

Factor out r^2:

r^2(28pi+4pi)=36pi

r^2(32pi)=36pi

r^2=(36pi)/(32pi)=9/8

Area of cylinder base:

A=pir^2=pi(9/8)=(9pi)/8