Question about masses and particles(modern physics)

[tarekkkkk]

if a system of particles is composed of n freely moving particles .is the mass of this system qual to the sum of the masses of the individual particles ?
well of course no but the idea is those particles if they are freely moving so there is empty spaces and if there an empty space that those particles didnt complete the total mass of the system so i think M(s)= M(holes) + M(particles that are moving) +M(particles that are at rest) please tell me what I am missing here thank you...

 

[tarekkkkk]

ok now what can i do hmm PLEASE HELP...

 

[tarekkkkk]

sorry i was talking bla bla but the answer is E=k.e+p.e ,p.e=... ,k.e=... from those u can get M=km hahahah see...