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11.02 Volume of prisms and cylinders

Lesson

Prisms

Volume is the amount of space taken up by a $3$3D object. While there are many specific formulas for particular prisms, in general, we can always come back to the formula below.

Volume of a prism
$\text{Volume of any prism }$Volume of any prism $=$= $\text{Area of Base }\times\text{Height }$Area of Base ×Height
$V$V $=$= $A_{base}\times h$Abase×h

Practice questions

Question 1

Find the volume of the cube shown.

A three-dimensional cube with edges depicted in a green outline. The front bottom edge of the cube is labeled with the measurement of $12$12 cm.

Question 2

Find the volume of the prism by finding the base area first.

A three-dimensional trapezoid prism is depicted. The trapezoid is facing front. The trapezoid has a bottom base measuring 16 cm, and a top base measuring 13 cm. The height of the trapezoid is measured 5 cm. The depth of the shape is measured 3 cm.

 

Cylinders

A cylinder is very similar to a prism (except for the lateral face), so the volume can be found using the same concept we have already learned.

Volume of a cylinder
$\text{Volume of Cylinder }$Volume of Cylinder $=$= $\text{Area of Base }\times\text{Height of Prism }$Area of Base ×Height of Prism
$\text{Volume of Cylinder }$Volume of Cylinder $=$= $\pi r^2\times h$πr2×h
$\text{Volume of Cylinder }$Volume of Cylinder $=$= $\pi r^2h$πr2h

 

Worked example

Question 3

You are at the local hardware store to buy a can of paint. After settling on one product, the salesman offers to sell you a can that is either double the height or double the radius (your choice) of the one you had decided on for double the price. Assuming all cans of paint are filled to the brim, is it worth taking up his offer?

Think: If so, would you get more paint for each dollar if you chose the can that was double the radius or the can that was double the height?

Do:

Doubling the height: $h\to2h$h2h

Since the volume of a cylinder is given by the formula $\pi r^2h$πr2h, if the height doubles, the volume becomes $\pi r^2\times2h=2\pi r^2h$πr2×2h=2πr2h 

If we double the height, we double the volume.

Doubling the radius: $r\to2r$r2r

Whereas if the radius doubles, the volume becomes $\pi\left(2r\right)^2h=4\pi r^2h$π(2r)2h=4πr2h.

If we double the height, we quadruple the volume.

Reflect: We should take the offer for and double the radius of the paint can as we get four times the paint for double the cost.

 

Exploration

To see how changes in height and radius affect the volume of a can to different extents, try the following interactive. You can vary the height and radius by moving the sliders around.

 

Practice questions

question 4

Find the volume of a cylinder correct to one decimal place if its diameter is $2$2 cm and its height is $19$19 cm.

question 5

Find the volume of a cylinder with radius $7$7 cm and height $15$15 cm, correct to two decimal places.

question 6

 

Units for Volume

It is probably worthwhile to remind ourselves of the units that are often used for calculations involving volume.

Units for Volume

cubic millimeters = mm3

(picture a cube with side lengths of 1 mm each - pretty small this one!)

cubic centimeters = cm3

(picture a cube with side lengths of 1 cm each - about the size of a dice)

cubic meters = m3 

(picture a cube with side lengths of 1 m each - what could be this big?)

AND to convert to capacity - 1cm3 = 1mL

 

Practice questions

QUEstion 7

Find the volume of the figure shown.

A hexagonal prism is depicted and is cut in half horizontally to form two trapezoid prisms. Both trapezoids are oriented in opposite direction to each other, sharing a common base (the shorter base) that measures 5 cm, indicated by a dashed line. Each trapezoid has a longer parallel side opposite the shared base, measuring 14 cm, and two non-parallel sides that are not labeled. The distance between the parallel sides of each trapezoid is marked as 7 cm. The length of the hexagonal prism perpendicular to the bases is measured 3 cm.

question 8

A hole is drilled through a rectangular box forming the solid shown. Find the volume of the solid correct to two decimal places.

Outcomes

GEO-G.GMD.3

Use volume formulas for cylinders, pyramids, cones, and spheres to solve problems. ★

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