# Conservation of energy or conservation of momentum

• salami
In summary, the problem is about an inelastic collision between a bullet and a block on wheels with no friction or energy losses. The person is trying to find the velocity of the system after the collision using conservation of momentum and kinetic energy. However, since energy is not conserved in an inelastic collision, the two methods will result in different answers.
salami
OK this is about a bullet hitting a block on wheels (inelastic collision), no friction or energy losses in the problem.

I'm trying to find Velocity of the system after collision

Why is it that if I use conservation of momentum I get a different answer of V than if I used conservation of Kinetic energy.

Momentum
m1*v1=(m1+m2)*v2

K energy
0.5*m1*v1^2=0.5*(m1+m2)*v2^2

You can make up your own numbers...I just don't understand the physics!

It's an inelastic collision--energy is not conserved. Mechanical energy will be lost.

The reason you get different numbers is that mechanical energy is NOT conserved in an inelastic collision, while momentum is.

## 1. What is conservation of energy?

Conservation of energy is a fundamental principle in physics that states that energy cannot be created or destroyed, but can only be transformed from one form to another. This means that the total amount of energy in a closed system remains constant over time.

## 2. How does conservation of energy apply to everyday life?

In everyday life, conservation of energy can be seen in many ways. For example, when you turn on a light bulb, electrical energy is converted into light and heat energy. The total amount of energy in the system (the light bulb and the surrounding environment) remains the same.

## 3. What is conservation of momentum?

Conservation of momentum is another fundamental principle in physics that states that the total momentum of a closed system remains constant over time. Momentum is a measure of an object's mass and velocity, and is conserved in collisions and other interactions between objects.

## 4. How is conservation of momentum related to Newton's laws of motion?

Conservation of momentum is closely related to Newton's laws of motion, particularly the third law which states that for every action, there is an equal and opposite reaction. This means that in any interaction between objects, the total momentum before and after the interaction remains the same.

## 5. Why are conservation laws important in science?

Conservation laws, such as conservation of energy and conservation of momentum, are important in science because they help us understand and predict the behavior of physical systems. They provide a framework for understanding how energy and momentum are transferred and transformed in various processes, and are essential in many areas of physics, from mechanics to thermodynamics to electromagnetism.

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