Which of the following statements are true? (Select allthatapply.)
1. For the total linear momentum of a system to be conserved,theremust be no external forces acting on the system.
2. The total linear momentum of a system may be conserved evenwhenthe mechanical energy of the system is not.
3. The velocity of the center of mass of a system changes onlywhenthere is a net external force on the system.
4. None of these statements are true.
I thought that the 1 was true because of the law of conservationofmomentum and 3 was true because if the total momentum of asystemremains constant, then the velocity of the center of mass ofthesystem remains constant, and you need an external force tochangemomentum.
I also though 2 was false.
However, I am being told this is wrong. Can someone clarify thisforme?