Key 1.7 JDL (1)

# Key 1.7 JDL (1) - iron is 4 inches on each side and thus...

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Key for Micro Exam 1 Question 7 JDL edit Question 7: (Try this problem on paper without a calculator. Make appropriate approximations where necessary to choose the logical answer from the choices below.) The density of iron is approximately 8 g/cm 3 . How much will a cubic piece of iron which is 4 inches on each side weigh in kg? (Hint: 1 inch is approximately 2.54 cm and 4 3 x2.5 3 is the same as (4 x 2.5) 3 ) Answers: (a) 1 kg (b) 4 kg (c) 8 kg (d) 12 kg (e) 16 kg (f) 12.3 kg (g) 4.165 kg This problem requires both dimensional analysis and a familiarity with the calculation of volume. We need to first calculate the volume of the piece of iron in question and then use dimensional analysis to calculate its weight in kg. The volume of an object is the product of its length, height, and width (V = lwh). Knowing this, we can arrange the problem using dimensional analysis in the pattern suggested below. The 4 is cubed because the cubic piece of
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Unformatted text preview: iron is 4 inches on each side and thus the volume = 4 x 4 x 4. However, the density given is in g/cm 3 so we need to convert in 3 to cm 3 . The hint for the problem informs us that “1 inch is approximately 2.54 cm”. We can then equate 1 in 3 with 2.54 3 cm 3 . It is critical that we cube 2.54. 1 inch = 2.54 cm and 1 in 3 = 2.54 3 cm 3 . While this problem may look like it needs a calculator at this point, you can use the second half of the hint to further help with the calculation, “4 3 x2.5 3 is the same as (4 x 2.5) 3 ).” This allows us to simplify the multiplication of the first two terms down to (4 x 2.5) 3 . 4 x 2.5 = 10 and 10 3 = 1000 which cancels out with the 1000 in the denominator and leaves you with 8 kg as the final answer. 4 3 in 3 | 2.54 3 cm 3 | 8 g iron| 1 kg = 8 kg | 1 in 3 | 1 cm 3 | 1000 g...
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## This document was uploaded on 11/04/2011 for the course CHEM 105 at BYU.

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