I want to ask what is the difference between conservation of momentum and conservation of ke, as using two equation, the answer will be different,
Take example, there is a bullet traveling 20ms-1 and 0.7 g, hit a cart of 1 kg, calculate the final velocity, the final answer by two equation is different, but both kinetic energy and momentum is conserved. I am so confused. Both seems correct, but different answer

Question

I want to ask what is the difference between conservation of momentum and conservation of ke, as using two equation, the answer will be different,
Take example, there is a bullet traveling 20ms-1 and 0.7 g, hit a cart of 1 kg, calculate the final velocity, the final answer by two equation is different, but both kinetic energy and momentum is conserved. I am so confused. Both seems correct, but different answer

anonymous · Answer

Can you show the steps for energy conservation for this problem ? I think you are not including final kinetic energy of the bullet.