Ncert Exercises & Solutions

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

F_{ext} = \frac{dp}{dt}

(from Newton's second law)

If F_{ext} = 0, dp = 0 \Rightarrow p = 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.