Find the area to be painted in the following block with a cylindrical hole. Given that length is 15 cm, width 12 cm, height 20 cm and radius of the hole 2.8 cm.
Solution:
The area to be painted consists of:
1)The four side walls of the block,
2) The top face of the block
3) The Bottom face of the block
1)The area of the four side walls are:
2 × (15 × 20) + 2 × (12 × 20)
= 600 + 480
=1080cm²
2) The area of the top and bottom face
= 2 × (12 × 15) - 2 × (π × 2.8²)
= 360 - 2 × (22/7) × 2.8 × 2.8
= 360 - 49.28
= 310.72cm²
The area to be painted = 1080 + 310.72 = 1390.72cm²
✦ Try This: Find the area to be painted in the following block with a cylindrical hole. Given that length is 15 cm, width 12 cm, height 20 cm and radius of the hole 3.5 cm.
The area to be painted consists of:
1)The four side walls of the block,
2) The top face of the block
3) The Bottom face of the block
1)The area of the four side walls are:
2 × (20 × 25) + 2 × (12 × 25)
= 1000 + 300
=1300cm²
2) The area of the top and bottom face
= 2 × (12 × 20) - 2 × (π × 3.5²)
= 480 - 2 × (22/7) × 3.5 × 3.5
= 480 - 77
= 403cm²
The area to be painted = 1300 + 403 = 1703cm²
☛ Also Check: NCERT Solutions for Class 8 Maths Chapter 11
NCERT Exemplar Class 8 Maths Chapter 11 Problem 100
Find the area to be painted in the following block with a cylindrical hole. Given that length is 15 cm, width 12 cm, height 20 cm and radius of the hole 2.8 cm.
Summary:
The area to be painted in the following block with a cylindrical hole, given that length is 15 cm, width 12 cm, height 20 cm and radius of the hole 2.8 cm, is 1390.72cm²
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