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Surface Areas and Volumes Test - 38

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Surface Areas and Volumes Test - 38
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  • Question 1
    1 / -0
    Edward bought a container of ceralac in the shape of cylinder. If the container has a radius $$10 m$$ and a surface area is $$\displaystyle 340\pi $$. What is its height?
    Solution
    Surface area of cylinder is $$A=2πr(r+h)$$

    Here the cylindrical container has surface area $$A=340π$$ m$$^2$$ and radius $$r=10$$ m.

    Thus,

    $$A=2πr(r+h)\\ \Rightarrow 340π=2π\times 10(10+h)\\ \Rightarrow 340π=20π(10+h)\\ \Rightarrow 340π=200π+20πh\\ \Rightarrow 20πh=340π-200π\\ \Rightarrow 20πh=140π\\ \Rightarrow h=\dfrac { 140π }{ 20π } =7$$

    Hence, the height of the cylindrical container is $$7m$$.
  • Question 2
    1 / -0
    The surface area of a cylindrical box is $$\displaystyle 132\ { mm }^{ 2 }$$ and its height is $$4 \ mm.$$ Find its radius.
    Solution
    Given: Cylindrical box has surface area $$A=132$$ $$mm^2$$ and height $$h=4\ mm$$

    We know surface area of cylinder is $$A=2πr(r+h)$$

    Thus, $$ 132=2\times \dfrac { 22 }{ 7 } \times r(r+4)$$

    $$ \Rightarrow 132=\dfrac { 44 }{ 7 } r(r+4)$$

    $$ \Rightarrow 132\times 7=44r(r+4)$$

    $$\Rightarrow 924=44r^{ 2 }+176r$$

    $$\Rightarrow 44r^{ 2 }+176r-924=0$$

    $$ \Rightarrow r^{ 2 }+4r-21=0$$

    $$ \Rightarrow r^{ 2 }+7r-3r-21=0$$

    $$ \Rightarrow r(r+7)-3(r+7)=0$$

    $$ \Rightarrow r+7=0,\quad r-3=0$$

    $$ \Rightarrow r=-7,\quad r=3$$

    Hence, the radius of the cylindrical box is $$3$$ mm.
  • Question 3
    1 / -0
    A skating board rocks back and forth on a wooden cylinder. The cylinder has a radius of 6 inches and a surface area is $$\displaystyle 590{ in }^{ 2 }$$. Find the height of the cylinder. ($$\displaystyle \pi =3.14$$).
    Solution
    Surface area of cylinder is $$A=2πr(r+h)$$

    Here the wooden cylinder has surface area $$A=590$$ in$$^2$$ and radius $$r=6$$ mm.

    Thus,

    $$A=2πr(r+h)\\ \Rightarrow 590=2\times \dfrac { 22 }{ 7 } \times 6(6+h)\\ \Rightarrow 590=\dfrac { 44 }{ 7 } (36+6h)\\ \Rightarrow 590\times 7=1584+264h\\ \Rightarrow 4130-1584=264h\\ \Rightarrow 264h=2546\\ \Rightarrow h=\dfrac { 2546 }{ 264 } =9.643$$

    Hence, the height of the wooden cylinder is $$9.65$$ in.

  • Question 4
    1 / -0
    Find the surface area of a cylinder with the following dimension:
    Height $$= 10$$ ft.
    Radius $$= 2$$ ft.
    Solution
    Surface area of cylinder is $$A=2πr(r+h)$$

    Here, radius is $$r=2$$ ft and the height is $$h=10$$ ft.

    Thus,

    $$A=2π\times 2(2+10)=2π\times 2\times 12=48π$$

    Hence, the surface area of the cylinder is $$48π$$ ft$$^2$$.

  • Question 5
    1 / -0
    Find the total surface area of the cylinder. (Use $$\displaystyle \pi =3.14$$).

    Solution
    Given: $$r=6ft$$ and $$h=12ft$$
    The total surface area of a cylinder = $$\displaystyle 2\pi r\left( r+h \right) $$
    $$\displaystyle =2\times 3.14\times 6\left( 6+12 \right) $$
    $$\displaystyle =2\times 3.14\times 6\left( 18 \right) $$
    $$=\displaystyle 678.24{ ft }^{ 2 }$$

    So, option D is correct.
  • Question 6
    1 / -0
    A gas cylinder has a diameter of $$14 $$m and height is  $$0.2$$m. Find its surface area. ($$\displaystyle \pi ={ 22 }/{ 7 }$$)
    Solution
    Surface area of cylinder is $$A=2πr(r+h)$$
    Here the gas cylinder has diameter $$14$$ m and therefore, the radius is half of diameter that is $$r=7$$ m and height $$h=0.2$$ m.
    Thus,
    $$A=2πr(r+h)=2 \times \dfrac {22}{7}\times 7(7+0.2)=316.512$$
    Hence, the surface area of the gas cylinder is $$316.512m^2$$.
  • Question 7
    1 / -0
    The curved surface area of a cylinder is $$\displaystyle 188.4\ { m }^{ 2 }$$. The height is $$12\ m$$. What is the radius? (use$$\displaystyle \pi =3.14$$).
    Solution
    Curved surface area of cylinder is $$A=2πrh$$

    Here, the curved surface area is $$A=188.4\ m^2$$ the height is $$h=12\ m$$.

    Thus,

    $$A=2πrh\\ \Rightarrow 188.4=2\times 3.14\times r\times 12\\ \Rightarrow 188.4=75.36r\\ \Rightarrow r=\dfrac { 188.4 }{ 75.36 } =2.5$$

    Hence, radius of the cylinder is $$2.5\ m$$
  • Question 8
    1 / -0
    Find the volume of a sphere whose diameter is  $$7.2\ mm$$.
    Solution
    Formula:
    Volume of sphere $$=\dfrac{4}{3} \pi r^3$$
                                   $$r=radius$$
    Given:
    $$diameter(d)=7.2\ mm$$

    $$radius(r)=\dfrac{d}{2}=\dfrac{7.2}{2}=3.6\ mm$$

    $$\Rightarrow \dfrac{4}{3} \pi  r^3=\dfrac{4}{3}\times 3.14\times (3.6)^3$$
                     
                     $$=\dfrac{4}{3}\times 3.6\times 3.6\times 3.6\times 3.14$$
                 
                     $$=\dfrac{4}{3}\times 46.656times 3.14$$

                     $$=\dfrac{585.999}{3}$$

                     $$=195.33\ mm^3$$
  • Question 9
    1 / -0
    What is the volume of a sphere? (use $$\displaystyle \pi =3.14$$)

    Solution
    Formula:
    Volume of sphere$$=\dfrac{4}{3}\pi r^3$$
    where,
    $$r=radius$$
    Given:
    $$r=11.8$$
    After substituting the values in the formula we
    $$ \dfrac{4}{3}\pi r^3             =\dfrac{4}{3}\times 3.14\times 11.8^3$$
               $$=\dfrac{4}{3}\times3.14\times11.8\times11.8\times11.8$$

                $$=\dfrac{20636.481}{3}$$
                $$=6878.82\ in^3$$
  • Question 10
    1 / -0
    The volume of a sphere is $$\displaystyle 1150.35{ in }^{ 3 }$$. Find its radius. (Round off your answer to the nearest whole number).
    Solution
    Formula:
    Volume of sphere$$=\dfrac{4}{3}\pi r^3$$
    where,
    $$r=radius$$
    Given:
    $$volume=1150.35\ in^3$$
    After substituting the values in the formula we get:
    $$1150.35= \dfrac{4}{3}\pi r^3$$

    $$\Rightarrow 1150.35= \dfrac{4}{3}*3.14* r^3$$

    $$\Rightarrow \dfrac{1150.35*3}{4*3.14}=r^3$$

    $$\Rightarrow r^3=\dfrac{3451.05}{12.56}$$
    $$\Rightarrow r^3=274.76$$
    $$\Rightarrow r=\sqrt[3]{274.76}$$
    $$\Rightarrow r=6.50\approx 7\ in$$
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