Density, Young's Modulus , Ultimate Strength: Synthesis Question

[SaintJude]

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I'm having great difficulty understanding the answer, especially regarding choice II.

Which of the following statements concerning the materials listed in the table above are true?

I. A greater force is required to rupture an aluminum rod than a glass rod

II. A unit of mass of bone would occupy a larger volume than a unite mass of glass.

III. When subjected to equal stress, bone would experience a greater strain than aluminum

A.I & II only
B. I & III only
C. II& III only
D. I, II, and III

Answer: A

 

[shoehornlettuce]

I'm having great difficulty understanding the answer, especially regarding choice II.

Which of the following statements concerning the materials listed in the table above are true?

I. A greater force is required to rupture an aluminum rod than a glass rod

II. A unit of mass of bone would occupy a larger volume than a unite mass of glass.

III. When subjected to equal stress, bone would experience a greater strain than aluminum

A.I & II only
B. I & III only
C. II& III only
D. I, II, and III

Answer: A

II is true because density is weight per unity volume. So lets say you have 1kg of bone and 1 kg of glass. For glass: 2200 = 1kg / Vglass and Vglass will = 1/2200. For bone: 1900 = 1kg / Vbone and Vbone will = 1/1900. 1/1900 is greater than 1/2200 so II is true.

 

[chiddler]

and I is true because ultimate strength tells you the threshold of force that they can take till breaking. Aluminum simply has a greater value.

III is false because stress/strain = young modulus. therefore, a larger YM means less strain per stress. (because they are inversely related)

bone has larger YM therefore less strain per stress.