Conservation of Mechanical Energy and Momentum in total inelastic collisions?

In summary, conservation of mechanical energy and momentum are conserved in total inelastic collisions.
  • #1
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Conservation of Mechanical Energy and Momentum in total inelastic collisions?

In an inelastic collision, such as a bullet getting stuck in a block hanging on a string, has two types of conservations?

-Total Inelastic Collisision Conservations:
(1) Conservation of Mechanical Energy: Uo+Po = U + P

(2) Conservation of Total Momentum: (m_1)(v_1a) = (m_1 + m_2)*v_b

-Questions:
1. Every time (or majority of the time) I am working with a total inelastic collision problem, must I use these two equations or at least consider them first.
2. I read that the conservation of energy is not conserved in total inelastic collisions, then how is it that the total kinetic energy is?
3. How is the conservation of total momentum conserved? Is it by taking into the account the initial momentum of the objects before the collision and the momentum of the objects as they are stuck together? I don't know if I am asking this right. I just want more insight into collisions inelastic/elastic.
 
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  • #2


Energy is conserved, but specific forms of it need not be as they can be converted to other forms. In an inelastic collision, some kinetic energy is converted to something else, usually heat.
Momentum is conserved - it takes no form other than a kinetic one.
"Instantaneously", the momentum of the bullet becomes shared between the bullet and the block, but subsequently some will pass to the string etc.
 
  • #3


I understand the concept of conservation of energy: that it can neither, created nor destroyed...thus in the case of the collision that it has to go to some other system if its not in our system of interest such as the collision itself (thus energy leaving our system in the form of heat). The conversion of energy to other forms, such as heat, when their is an inelastic collision, is this an internal energy of a system (what's the difference between in an external- vs internal- system)? I'm having a hard time relating it to real world situations...
 
  • #4


The bullet and block would become hot. This is still a form of kinetic energy in reality, but it's now the random jiggling of molecules. This is not considered mechanical energy since it is not easily used for mechanical purposes.
 
  • #5


Ok, thanks for talking physics with me...I need to get this Physics jargon down cus I'm struggling with this. All tips and info help at this point, so thanks again.
 

1. What is the definition of total inelastic collisions?

Total inelastic collisions are collisions between two objects in which they stick together and move as one object after the collision. In these collisions, kinetic energy is not conserved and is converted into other forms of energy, such as sound or thermal energy.

2. How is conservation of mechanical energy applied in total inelastic collisions?

In total inelastic collisions, mechanical energy (the sum of kinetic and potential energy) is not conserved. However, the total momentum of the system before and after the collision remains the same. This is known as the conservation of momentum.

3. What is the equation for conservation of mechanical energy in total inelastic collisions?

The equation for conservation of mechanical energy in total inelastic collisions is: m1v1 + m2v2 = (m1 + m2)v, where m1 and m2 are the masses of the objects, v1 and v2 are their velocities before the collision, and v is the final velocity of the combined object after the collision.

4. How does the coefficient of restitution affect the conservation of mechanical energy in total inelastic collisions?

The coefficient of restitution, which represents the ratio of the final to initial relative velocities of two objects, is zero in total inelastic collisions. This means that the objects stick together and move with a common final velocity, resulting in a loss of kinetic energy.

5. Can the conservation of mechanical energy be violated in total inelastic collisions?

No, the conservation of mechanical energy cannot be violated in any type of collision, including total inelastic collisions. While the total mechanical energy may change form, the total amount of energy in the system remains constant.

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