Question : A metallic solid spherical ball of radius 3 cm is melted and recast into three spherical balls. The radii of two of these balls are 2 cm and 1.5 cm. What is the surface area (in cm2) of the third ball?
Option 1: $50 \pi$
Option 2: $\frac{25}{4} \pi$
Option 3: $25 \pi$
Option 4: $\frac{25}{2} \pi$
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Correct Answer: $25 \pi$
Solution : Let the radius of the smaller balls be r1, r2, and r3. The radius of the larger sphere is r. So, $\frac{4}{3}\pi$r3 = $\frac{4}{3}\pi$(r13 + r23 + r33) ⇒ r3 = r13 + r23 + r33 ⇒ 33 = 23 + 1.53 + r33 ⇒ 33 = 8 + 3.375 + r33 ⇒ r33 = 27 – 8 – 3.375 ⇒ r33 = 15.625 ⇒ r3 = 2.5 The surface area of the third ball = 4$\pi$r32 = 4$\pi$(2.5)2 = 25$\pi$ cm2 Hence, the correct answer is $25\pi$.
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Question : A spherical ball of lead, 3 cm in diameter, is melted and recast into three spherical balls. The diameters of two of these balls are $\frac{3}{2}$ cm and 2 cm, respectively. Find the diameter of the third ball.
Option 1: 2.1 cm
Option 2: 3.3 cm
Option 3: 3 cm
Option 4: 2.5 cm
Question : The sum of the curved surface area and the total surface area of a solid cylinder is 2068 cm2. If the radius of its base is 7 cm, then what is the volume of this cylinder? (use $\pi=\frac{22}{7}$)
Option 1: 2060 cm3
Option 2: 2480 cm3
Option 3: 3080 cm3
Option 4: 2760 cm3
Question : The curved surface area of a solid hemisphere is 22 cm2. What is the total surface area of the hemisphere? (use $\pi=\frac{22}{7}$)
Option 1: 66 cm2
Option 2: 44 cm2
Option 3: 33 cm2
Option 4: 30 cm2
Question : The radius of a large solid sphere is 14 cm. It is melted to form 8 equal small solid spheres. What is the sum of the total surface areas of all 8 small solid spheres? (use $\pi=\frac{22}{7}$)
Option 1: 3648 cm2
Option 2: 4928 cm2
Option 3: 4244 cm2
Option 4: 4158 cm2
Question : Three solid metallic spheres of radii 1 cm, 6 cm, and 8 cm, respectively, are melted and recast into a single solid sphere. The radius of the new sphere formed is:
Option 1: 9.0 cm
Option 2: 5.9 cm
Option 3: 7.7 cm
Option 4: 8.5 cm
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