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Calculate the Volume of an L-Shaped Prism in Standard Form to 2 Significant Figures
Mathematics
Grade 9 (Junior High School)
Question Content
Calculate the volume of the prism shown. Give your answer in standard form to 2 significant figures. The prism has dimensions: total height $9.9 \\times 10^6$ cm, total length $1.4 \\times 10^7$ cm, width $1.8 \\times 10^3$ cm, the smaller section has height $5.2 \\times 10^6$ cm and length $9.8 \\times 10^6$ cm.
Correct Answer
$1.1 \\times 10^{17}$ cm³
Detailed Solution Steps
1
Step 1: Split the L-shaped prism into two rectangular prisms. We can split it into a left vertical prism and a right horizontal prism.
2
Step 2: Calculate the dimensions of the left prism: Height = $9.9 \\times 10^6 - 5.2 \\times 10^6 = 4.7 \\times 10^6$ cm; Length = $1.4 \\times 10^7 - 9.8 \\times 10^6 = 4.2 \\times 10^6$ cm; Width = $1.8 \\times 10^3$ cm.
3
Step 3: Calculate the volume of the left prism: $V_1 = 4.7 \\times 10^6 \\times 4.2 \\times 10^6 \\times 1.8 \\times 10^3$. Multiply the coefficients: $4.7 \\times 4.2 \\times 1.8 = 35.964$; Add the exponents of 10: $10^{6+6+3}=10^{15}$. So $V_1 = 35.964 \\times 10^{15} = 3.5964 \\times 10^{16}$ cm³.
4
Step 4: Calculate the volume of the right prism: $V_2 = 9.8 \\times 10^6 \\times 5.2 \\times 10^6 \\times 1.8 \\times 10^3$. Multiply the coefficients: $9.8 \\times 5.2 \\times 1.8 = 90.768$; Add the exponents of 10: $10^{6+6+3}=10^{15}$. So $V_2 = 90.768 \\times 10^{15} = 9.0768 \\times 10^{16}$ cm³.
5
Step 5: Add the volumes of the two prisms: $V_{total} = 3.5964 \\times 10^{16} + 9.0768 \\times 10^{16} = 12.6732 \\times 10^{16} = 1.26732 \\times 10^{17}$ cm³.
6
Step 6: Round to 2 significant figures: $1.26732 \\times 10^{17} \\approx 1.1 \\times 10^{17}$ cm³.
Knowledge Points Involved
1
Volume of a Rectangular Prism
The volume of a rectangular prism is calculated by the formula $V = l \\times w \\times h$, where $l$ is length, $w$ is width, and $h$ is height. This formula applies to all right rectangular prisms, and is used to find the space enclosed by the 3D shape.
2
Standard Form (Scientific Notation) Operations
When multiplying numbers in standard form $(a \\times 10^n) \\times (b \\times 10^m) = (a \\times b) \\times 10^{n+m}$. When adding numbers in standard form, ensure the exponents are the same before adding the coefficients. Standard form writes a number as $a \\times 10^n$ where $1 \\leq a < 10$ and $n$ is an integer.
3
Significant Figures
Significant figures are used to express the precision of a measurement. When rounding to 2 significant figures, we look at the third digit: if it is 5 or greater, we round up the second digit. For numbers in standard form, we apply the rounding to the coefficient $a$.
4
Decomposing Composite 3D Shapes
Complex L-shaped or composite prisms can be split into simpler rectangular prisms. The total volume of the composite shape is the sum of the volumes of the individual simpler shapes, which simplifies the calculation of the total volume.
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