A solid sphere of radius 8 cm is melted and then recast into small spherical balls each of diameter 4 cm. Find the number of balls thus obtained (use ).
Show answer & explanation
Correct answer: B
Explanation
The correct answer is option 2 i.e. 64.
Short Trick:
The total number of small spherical balls = R3/r3 = = 64
Alternate method:
The volume of a sphere = (4/3)πr3, where r is the radius.
The radius of the large sphere (R) = 8 cm
Volume of the large sphere = (4/3)π(83) = (4/3)π(512) = (2048/3)π cm3
The diameter of each small sphere = 4 cm
So, the radius of each small sphere (r) = 2 cm
Volume of each small sphere = (4/3)π(23) = (4/3)π(8) = (32/3)π cm3
Number of small spheres = = 64
Therefore, 64 small spherical balls can be obtained.