document.write( "Question 1125312: GENERAL: Hailstones A hailstone (a small sphere of ice) is forming in the clouds so that its radius is growing at the rate of 1 millimeter per minute. How fast is its volume growing at the moment when the radius is 2 millimeters? [Hint: The volume of a sphere of radius r is V = 4/3*pi r^3.] \n" ); document.write( "
Algebra.Com's Answer #741607 by ikleyn(52803)\"\" \"About 
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document.write( "You are given  V(t) = V(r(t)) = \"%284%2F3%29%2Api%2Ar%28t%29%5E3\",  where the radius  r  varies  such that  \"%28dr%29%2F%28dt%29\" = 1 millimeter per minute.\r\n" );
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document.write( "Then  \"%28dV%29%2F%28dt%29\" = \"4%2Api%2Ar%5E2\".\"%28dr%29%2Fdt%29\" = \"4%2A3.14%2A2%5E2\".\"1\" = 4*3.14*4 = \"16pi\" = 50.24 mm^3 per minute.\r\n" );
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document.write( "Thus the instantaneous volume growing rate is  50.24 mm^3/minute.\r\n" );
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document.write( "Interesting, that if you calculate the averaged volume growing rate between  t= 2 seconds  and  t= 3 seconds, you will get another value\r\n" );
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document.write( "\"%28V%283%29+-+V%282%29%29%2F%283-2%29\" = \"%284%2F3%29%2Api%2A3%5E3\" - \"%284%2F3%29%2Api%2A2%5E3\" = \"%284%2F3%29%2Api%2A%2827-8%29\" = \"%2876%2F3%29%2Api\" = \"%2876%2F3%29%2A3.14\" = 79.55  mm^3/minute.\r\n" );
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document.write( "But it only demonstrates the difference between these two conceptions: instantaneous and averaged rates.\r\n" );
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\n" ); document.write( "\n" ); document.write( "Answer.   The instantaneous volume growing rate at this moment is  50.24 mm^3 per minute.\r
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