Weight of Sculpture Story Problem

geekily

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Jan 24, 2007
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A sculpture made of iron has the shape of a right square prism topped by a sphere. The metal in each part of the sculpture is 2 mm thick. If the dimensions are as shown and the density of the iron is 7.87 g/cm^3, calculate the approx. weight of the sculpture in kilograms.

It shows a sphere with a radius of 18 cm, and a square prism with dimensions of 40 cm x 40 cm x 1 m. First, I figured out the volume of each: 7776pi cm^3 for the sphere and 160000 cm^3 for the prism. Now I'm stuck. I've been experimenting multiplying both numbers by .2 since the metal is 2 mm thick and multiplying by 7.87 g, which I know would have to then be turned in to kg, and pretty much every combination of things I could think of. The correct answer is 36.3 kg, according to the key, but I can't seem to get anywhere near that. What am I doing wrong?

Thanks for your help!
 
geekily said:
A sculpture made of iron has the shape of a right square prism topped by a sphere. The metal in each part of the sculpture is 2 mm thick. If the dimensions are as shown and the density of the iron is 7.87 g/cm^3, calculate the approx. weight of the sculpture in kilograms.

It shows a sphere with a radius of 18 cm, and a square prism with dimensions of 40 cm x 40 cm x 1 m. First, I figured out the volume of each: 7776pi cm^3 for the sphere and 160000 cm^3 for the prism.

These are hollow structures

so the volume of the (hollow) prism is = [1600000 - (39.6)*(39.6)*(999.6)] cm^3

similarly find volume of the hollow sphere - and continue....

Now I'm stuck. I've been experimenting multiplying both numbers by .2 since the metal is 2 mm thick and multiplying by 7.87 g, which I know would have to then be turned in to kg, and pretty much every combination of things I could think of. The correct answer is 36.3 kg, according to the key, but I can't seem to get anywhere near that. What am I doing wrong?

Thanks for your help!
 
Ah, okay, I think that was my problem - I wasn't thinking of it as a hollow object. Thanks so much!
 
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