# The center of mass of a system of particles is at the origin from this we conclude that

a) the number of particles on the positive X axis is equal to the number of paticles on the negative x-axis.

b) the total mass of the particles on the positive x-axis is the same as the total mass on negative x-axis.

c) the number of particles on the x-axis may be equal to the number of particles on the y axis.

d) If there is a particle on the positive X axis, there must be at least one particle on the negative x-axis.

The masses of the particles need not be the same.
Hence b is not possible.
The positions of the particles may be different.
Hence a is not possible.
d is not necessary because it is enough if the x coordinate is negative
answered Nov 20, 2013 by
edited Jun 16, 2014