Give your answer to 1 decimal place
Volume of a prism — Notes & Worked Examples Show / Hide
Explanation:
A prism is a 3D shape that has the exact same 2D shape (the cross-section) running all the way through its length. For any prism: Volume of Prism = Area of Cross-Section × Length.
Always calculate the area of the front cross-section first (whether it is a triangle, a trapezium, or a compound L-shape), and then multiply that area by the depth/length of the prism.
Example 1: A triangular prism has base 8 cm, perpendicular height 6 cm, and length 12 cm. Find its volume.
Example 2: A prism has a trapezium cross-section with parallel sides 5 m and 9 m, height 3 m, and length 10 m. Find its volume.
Give your answer to 1 decimal place
Worked Solution & Answer
Worked Solution & Answer
Area of L-shaped cross-section = (2 × 3) + (1 × 1) = 7 cm² M2
Volume = 7 × 6 = 42 cm³. A1
The height of trapezium ABCD is h cm
The volume of the prism is 608 cm3
Work out the value of h.
Worked Solution & Answer
0.5 × (7 + 12) × h × 10 = 608 M1
⇒ 95h = 608 M1
⇒ h = 608 ÷ 95 = 6.4 A1
The volume of the prism is 28 m3
The pressure on the floor due to the prism is 65 newtons/m2
Work out the force exerted by the prism on the floor.
Worked Solution & Answer
Base area = Volume ÷ height = 28 ÷ 4 = 7 m² M2
Force = pressure × area = 65 × 7 = 455 newtons A1
The box is in the shape of a triangular prism.
Worked Solution & Answer
It is made by cutting a solid cube of side 2 cm in half.
Worked Solution & Answer
Volume of cube = 2 × 2 × 2 = 8 cm³ M2
Volume of prism = 8 ÷ 2 = 4 cm³. A1
(a) Calculate the area of the triangle.
(b) The triangle is the cross-section of the prism shown.
Calculate the volume of the prism.
(c) Another triangular prism has the same cross-section as the one in (b).
The length of the prism is 50 mm.
Without finding the volume of this prism, explain why it has a greater volume than the prism in part (b).
Calculate the volume of the prism. [1 mark]
The length of the prism is 50 mm.
Without finding the volume of this prism, explain why it has a greater volume than the prism in part (b). [1 mark]
Worked Solution & Answer
Area = 12 × base × height = 12 × 8 × 5.5 = 22 cm2 M1 A1
Volume = Area of cross-section × length = 22 × 4.5 = 99 cm3 B1
50 mm = 5 cm > 4.5 cm
Since cross-sectional area is identical, volume is directly proportional to length. B1
Work out the volume of the prism.
Give your answer correct to 3 significant figures.
Worked Solution & Answer
Roof triangle height h = 5 × tan 40° = 4.1955 cm M2
Area of cross section = (10 × 12) + (0.5 × 10 × 4.1955) = 120 + 20.977 = 140.977 cm² M2
Volume = 140.977 × 25 = 3524.4 cm³ = 3520 cm³ (3 s.f.) A1
Worked Solution & Answer
From the side elevation, the prism is 6 cm long
The plan is a 6 cm by 4 cm rectangle split into a 6 cm by 1 cm strip and a 6 cm by 3 cm strip. A1
Area of pentagonal cross-section (front elevation) = (4 × 1) + (1 × 2) + (12 × 3 × 2) = 4 + 2 + 3 = 9 cm2 M1
Length of the prism = 6 cm M1
Volume = cross-sectional area × length = 9 × 6 = 54 cm3. A1