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The circumference of a circle of radius r cm is 2*pi*r cm so the length of the semi-circular arc is pi*r cm. The length of the diameter is 2*r cm so the total length is (pi + 2)*r cm
The formula for finding the volume of a cone is 1/3(pi)(r)(r)(h) where r is the radius and his the height, or in your case, 1/3(B)(h) where B is the area of the base and h is the height since part of the original formula is finding the base area [(pi)(r)(r)]. Plug your measurements into your calculator and you get 76 2/3 pi square cm, or 240.7 square cm.
The area of a circle with radius r is pi*r*r where pi = 3.1416 approx. When r = 6 cm, the area is 113.1 sq cm.
A US 5 cent coin (a nickel) has a diameter of 21.21 mm -. That is 2.121 cm
r = 75.36 cm