SOLUTION: The ball of a float valve has a diameter of 4 in., and the thickness of the metal is 0.05 in. How much does it weigh if it is made of copper? (Copper weighs 556 lb. per cu. ft.)

Question 1181645: The ball of a float valve has a diameter of 4 in., and the thickness of the metal is 0.05 in. How much does it weigh if it is made of copper? (Copper weighs 556 lb. per cu. ft.)
Found 2 solutions by mananth, ikleyn:
Answer by mananth(16946)   (Show Source): You can put this solution on YOUR website!
Outer volume - inner volume = volume of copper.
Volume of copper * density of copper = weight of copper
outer radius = 2 "
inner radius = 2- 0.05 = 1.95 "
Volume of copper= (4/3)*pi * (2-1.95)^3
V= 0.000523 in^3
556 lb/ft^3= 5.15 ounce/in^3
Weight of copper = 0.000523* 5.15
= 0.0027 ounces
Answer by ikleyn(52781)   (Show Source): You can put this solution on YOUR website!
.

            The solution by @mananth is FATALLY INCORRECT !

            It contains a FATALL ERROR !

            If to combine all incorrect solutions/answers by @mananth at this forum,
            it would comprise an entire book showing all possible and typical errors
            and teaching on how Math problems should not be solved at any circumstances !

            See my correct solution below.

Outer volume - inner volume = volume of copper. Volume of copper * density of copper = weight of copper outer radius = R = 2 inches inner radius = r = 2- 0.05 = 1.95 inches. Volume of copper = - = V= 2.449 in^3 556 lb/ft^3 = 0.322 lb/in^3 Weight of copper = 2.449 * 0.322 = 0.789 pounds. ANSWER

            Notice that the correct answer is about 5000 times the incorrect answer by @mananth   ( ! )   ( ! ! )   ( ! ! ! )

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