Conservation of momentum in a collision between particles can be understood from:

1. conservation of energy
2. newton's first law only
3. newton's second law only
4. both Newton's second and third law
(d)
Hint: When there is no external force in the system, the linear momentum of the system remains conserved.
Step 1: Apply Newton's second law of motion.
We know that for a system        Fext=dpdt                     (from Newton's second law)
 If Fext=0,dp=0p= constant 
Hence, the momentum of a system will remain to conserve if an external force on the system is
In case of collision' between particles equal and-opposite forces will act on individual particles by Newton's third law,
Hence total force on the system will be zero.