A metallic hollow cylindrical pipe has outer and inner radii as 6 cm and 4 cm respectively. Find the volume of the metal used in the pipe of length of 14 cm.
A cubical block of side 7 cm is surmounted by a hemisphere of largest possible diameter as shown in Figure 1. Find the total surface area of the solid.
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Answer: 332.5 cm2
Largest hemisphere has diameter 7 cm, so r=3.5 cm.
TSA = surface area of cube − area of base circle of hemisphere + curved surface area of hemisphere
A cubical block of side 7 cm is surmounted by a hemisphere of largest possible diameter as shown in Figure 2. Find the total surface area of the solid.
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Answer: 332.5 cm2
Largest hemisphere has diameter 7 cm, so r=3.5 cm.
TSA = surface area of cube − area of base circle of hemisphere + curved surface area of hemisphere
A solid is in the shape of a cone standing on a hemisphere with both their radii being equal to 1 cm and the height of the cone is equal to its radius. Find the volume of the solid in terms of π.
A solid metallic sphere of radius 10.5 cm is melted and recast into a number of smaller cones, each of radius 3.5 cm and height 3 cm. Find the number of cones so formed.
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Answer: 126
Volume of sphere =34π(10.5)3.
Volume of one cone =31π(3.5)2(3).
Number of cones =31π(3.5)2×334π(10.5)3=3.5×3.5×34×10.5×10.5×10.5
A cone of height 28 cm and radius of base 7 cm is made up of modelling clay. A child reshapes it in the form of a sphere. Find the radius of the sphere.
A solid piece of metal in the form of a cuboid of dimensions 11 cm × 7 cm × 7 cm is melted to form ‘n’ number of solid spheres of radii 27 cm each. Find the value of n.
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Answer: n = 3
Volume of cuboid =11×7×7=539 cm3.
Volume of one sphere =34πr3=34×722×27×27×27=3539 cm3.
150 spherical marbles, each of diameter 1.4 cm, are dropped in a cylindrical vessel of diameter 7 cm containing some water, and are completely immersed in water. Find the rise in the level of water in the cylindrical vessel.
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Answer: 5.6 cm
Radius of each marble =0.7 cm; volume of 150 marbles =150×34π(0.7)3=200×0.343π=68.6π cm3.
Radius of vessel =3.5 cm. Let the water rise by h cm: π(3.5)2h=12.25πh.