# Conceptual Momentum/Energy Problem

• JB83
In summary, it is always true that two objects of different masses but moving at the same velocity will have different momentum. In an elastic collision, kinetic energy is conserved. However, in a perfectly inelastic collision, all kinetic energy is lost. The statement that momentum of a system may be conserved even when mechanical energy is not is false, as shown in the examples of inelastic collisions where some kinetic energy is lost.
JB83
Determine for each of the following statements whether it is always true or can be false.

Two objects of different masses but moving at the same velocity have different momentum.
-this should be true because p=mv and if there are different v then the p should be different.
Kinetic energy is conserved in an elastic collision.
-true
Momentum of a system may be conserved even when mechanical energy is not.
-false
In an elastic collision the momentum is conserved.
-true
In a perfectly inelastic collision, all the kinetic energy of the objects involved in the collision is lost.
-true

These are the answers I believe to be true. Does anyone have any idea why at least one of them is wrong?

Two of your answers are wrong. Here are some things to consider. (Imagine the collisions to take place on a frictionless surface):
(1) Say two identical chunks of clay, moving towards each other at the same speed, smack into each other and stick together. What kind of collision is this? What's conserved? What's not conserved? (This might give you a hint about one of your answers.)
(2) Say a chunk of clay, moving at some speed, smacks into another piece of clay that is at rest. They stick together. What kind of collision is this? What's conserved? What's not conserved? After the collision, does the clay still have kinetic energy? (This might give you another hint.)

Think of an inelastic collision and you will know why number three is wrong.

In the last one: think of the equation to find kinetic energy. If the velocity of both objects after the collision is not zero, then what would the kinetic energy be? Is it all lost?

[and I apparently posted at the same time as the the above poster. Heh...]

## 1. What is conceptual momentum/energy problem?

Conceptual momentum/energy problem is a physics problem that involves understanding the relationship between momentum and energy in a system. It requires conceptual understanding of these two concepts and their conservation in different scenarios.

## 2. How is momentum related to energy?

Momentum and energy are closely related in a system. Momentum is the measure of an object's motion, while energy is the ability to do work. In a closed system, the total momentum and total energy are conserved, meaning they cannot be created or destroyed, only transferred or transformed.

## 3. What are some examples of conceptual momentum/energy problems?

Some examples of conceptual momentum/energy problems include: a bouncing ball, a pendulum swinging, a car collision, a roller coaster ride, and a swinging door. These scenarios involve the conversion of energy into different forms and the conservation of momentum.

## 4. How can I solve a conceptual momentum/energy problem?

To solve a conceptual momentum/energy problem, you need to identify the initial and final states of the system, and determine the types of energy involved (kinetic, potential, etc.). Then, apply the principles of conservation of momentum and energy to set up equations and solve for the unknown variables.

## 5. Why is it important to understand conceptual momentum/energy problems?

Understanding conceptual momentum/energy problems is crucial for understanding the fundamental laws of physics and their applications in real-world scenarios. It also helps in problem-solving skills and critical thinking, which are useful in many fields, such as engineering, physics, and mechanics.

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