Four identical spheres each of radius 'a' are placed on a horizontal table touching one another so that their centres lie at the corners of a square of side 2a. Position of their centre of mass is :

Options

A. 2a, a
B. 3a, a
C. a, a
D. `a//2 a//2`

Answer

C

Explanation

Let .O. be the origin. Then

`x=(Mxx0+Mxx2a+M(2a)+Mxx0)/(M+M+M+M)=a`
Then `y=(Mxx0+Mxx0+Mxx2a+Mxx2a)/(M+M+M+M)=a`