General Physics General Physics Help Forum

 Aug 9th 2017, 05:15 AM #1 Member   Join Date: Mar 2013 Posts: 32 Demsity-Please help Density of a regular wooden block is 0,8 gr/cubic centimeters. The Mass of the wooden block is 800 grams. We hollow the wooden block and put melted iron into the hole with a density of 7,8 g/cubic centimeters.The Total mass of the system becomes 1.5 kilograms. Find the volume of the hole(hollow)? Answer is 100 but I can't find the answer. I found the volume of the block as 1000 cc. density=mass/volume 7.8=(1500-800)/V I found the answer as 90 but the answer is 100. Please help.
 Aug 9th 2017, 06:19 AM #2 Physics Team     Join Date: Jun 2010 Location: Morristown, NJ USA Posts: 2,320 You left out the fact that once the hole is cut in the wood the volume of wood remaining is less than 1000 cm^3. Let V = the volume of the hole, then the mass of the remaining wood is (1000 cm^3 - V) x 0.8 g/cm^3. The mass of the iron is V x (7.8 g/cm^3). So the equation is: (1000-V) x 0.7 + V x 7.8 = 1500 Solve for V.
 Aug 9th 2017, 11:36 AM #3 Member   Join Date: Mar 2013 Posts: 32 Many Thanks.

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