Statement
difficulty
A 3 Kg ball is moving towards left at 6 m/s. It collides with a 5 Kg ball moving towards right at 2 m/s. After the collision the second ball went through the left at 3 m/s. Calculate the velocity of the first ball after the crash.
Solution
Data
- First´s ball mass m1 = 3 kg
- Second´s ball mass m2 = 5 kg
- First´s ball velocity before the crash
- Second´s ball velocity before the crash
- Second´s ball velocity after the crash
Resolution
The linear momentum conservation principle establishes that, in absence of outer forces, the momentum is preserved. So, the linear momentum before the crash and after it must be the same.
The initial momentum of the system is made by the sum of momentums of each one of the balls:
The final momentum is given by:
We are ready now to solve the final velocity of the first ball: