Question

Two 1.5 kg balls approach each other with the same speed of 3.0 m/s . What is the total momentum nof the system by before collision?

Answer 1

Let the first ball moves in positive direction. its momentum is

$$p_1=mv$$

Thus, the second ball moves in negative direction. its momentum is

$$p_2=-mv$$

The total momentum nof the system before collision is

$$p=p_1+p_2=mv+(-mv)=0 kgm/s$$