<PRE><B>Question 20749</B>
Q: Pottery You are taking a pottery class.  As an assignment, you are given a lump of clay whose volume is 200 cubic cetimeters and asked to make a cylindrical pencil holder.  The pencil holder should be 9 centimeters high and have an inner radius of 3 centimeters.  What thickness x should your pencil holder have if you want to use all the clay?  (Hint: The volume of clay equals the difference of the volumes of two cylinders.)

Ans: 

Total Volume of hollow cylender V = 200 cc
Inner radius Ri = 3 Cm
Outer Radius Ro = r (Assume it)
Height of cylinder = 9 cm

Volume of Hollow Cylander=Volume of Outer Cylender - Volume Of inner Cylender 
                 so 200  = Pi*Ro*Ro*9 -  Pi*Ri*Ri*9
                         = Pi*9(Ro*Ro - 3*3)
             200/(3.14*9)= Ro*Ro -9
           200/28.26 + 9 = Ro*Ro
           7.077 + 9 = Ro*Ro
           16.077 = Ro*Ro
           4 = Ro    ----------(Taking square Root )
So thickness of the Cylinder = Ro-Ri (Outer Radius - Inner Radius)
                             = 4 - 3
                             = 1 cm</PRE>