The rectangular solid block of dimensions 20cm by 10cm by15cm. It has a cylindrical hole bored at it's centre. The mass of the block is 14.9kg and it is made of a material that has a densy of 5gcm³. What is cross sectional area of the hole in cm²?
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Jawaban:
583 cm^2
Penjelasan:
Let the ;ength, breadth, height of cuboidal block be 15 cm,10 cm, and 5 cm respectively.
Total surface area of solid cuboidal block
= 2(lb+bh+lh)
=2(15x10+10x5+15x5) cm^2
=2(150+50+75 )= 2(275) = 550 cm^2
Radius of cylindrical hole = r 7/2 cm
Area of two circular bases
= r^2 + r ^2 = 2 r^2
= 2 x 22/7 x 7/2 x 7/2 = 77 cm^2
Curved surface area ofcylinder = 2 rh
= 2 x 22/7 x 7/2 x 5 = 110 cm^2
Required area = (area of cuboidalblock - area of two circular bases + area of cylinder )
= (550+110-77) cm^2 = 583 cm^2