Answer:
>400N is needed to balance that lever
A scientific journal article that is peer reviewed. This is because it is more likely not have factual information and sources to that information.
B) law of conservation of momentum
It states that the total momentum of a system before impact is the same as the total momentum of the system after impact.
In this case total momentum before impact:
10kg*5m/s + 5kg * 0m/s = 50 kg m/s
After Impact:
10kg*0m/s + 5kg*10m/s = 50 kg m/s
You can see the momentum before and after impact is same as 50 kg m/s
Of course we assumed that the first cart stopped after the impact, and there are no energy losses.
It expands and pushes the crack further aprt