# Conservation of Momentum, Everygy, Etc

• tigerengineer
In summary: This is the second time you have failed to do so, so I'm going to have to ask you to do it again. Do not post until you have followed the template.In summary, True/False questions I got for homework, need some help making sure my answers are right.
tigerengineer
Here's some homework True/False questions I got for homework, need some help making sure my answers are right.

True/False:
1)In a collision between a laight hydrogen molecule and a heavy water molecule, the momentum lost by one molecule is exactly the same as the momentum gained by the other molecule.

2)Mechanical energy is conserved whenever momentum is conserved.

3)Kinetic energy is conserved only in perfectly elastic collisions, but momentum is conserved in all collisions.

4)Two cars collide, lock bumpers and eventually slide to a stop due to friction with the roadway. During this entire process, mechanical energy and momentum are both conserved.

5)If the dot product of two nonzero vectors is zero, those vectors must be perpendicular to each other.

6)When a moving object hits a stationary object and causes it to move, some of the moving object's kinetic energy is transformed into momentum in the object that was at rest.

1)T
2)F
3)F
4)T
5)F
6)T

But if you're going to be that much of a prick about it, just don't worry about it.

I'll just write out the logic/questions I'd have for each of them to suggest the answers I'd pick.

1) Linear momentum is conserved

2) First, what is your teaching meaning by "mechanical energy"? Momentum conservation doesn't imply any kind of energy conservation, it exists independently of energy conservation (each conservation law comes from a particular symmetry of the system), but I'd just be careful to make sure that this "mechanical energy" isn't being defined from momentum in some circular manner.

3) Well, yeah... that's basically just a statement about the type of system you are talking about.

4) I'm not a physicist, but I honestly don't know what "mechanical energy" is referring to in this context. This is an inelastic collision though...

5) Try coming up with some cases here...

6) I'm not honestly sure if this is just really sloppy terminology, or an elaborate trick question... I'd have to know the level that this question was being asked at to give a serious answer.

tigerengineer said:
1)T
2)F
3)F
4)T
5)F
6)T

But if you're going to be that much of a prick about it, just don't worry about it.

I agree with your answers to 1 and 2. but for the rest,

3 is true based on the principles of elastic collisions and conservation of momentum
4 is false if mechanical energy is referring to kinetic energy since energy is lost
5 is true - its just a basic principle of vectors
6 I am not too sure about- But I want to say false because of the way that it's worded.

I'm pretty sure of these answer, although I can't say that I'm 100% sure because of the weird way that theyre worded.

guitarguy1 said:
I agree with your answers to 1 and 2. but for the rest,

3 is true based on the principles of elastic collisions and conservation of momentum
4 is false if mechanical energy is referring to kinetic energy since energy is lost
5 is true - its just a basic principle of vectors
6 I am not too sure about- I want to say false because of the improper way that it's worded.

I'm pretty sure of these answer, although I can't say that I'm 100% sure because of the weird way that theyre worded.

Yeah, I agree here. The wording is incredibly poor in the original questions, but these should be the answers, within the assumption that this is high school level physics?

tigerengineer said:
1)T
2)F
3)F
4)T
5)F
6)T

But if you're going to be that much of a prick about it, just don't worry about it.

Nice attitude. Grow up.

The rules (that you agreed to when you signed up with this forum, by the way) say you must show your work before you can expect help. You did not do that, so I'm going to tell you to do it. Your post is typical of those you would expect from some lazy student looking for free answers.

The homework template is there for a reason, please use it.

## 1. What is the law of conservation of momentum?

The law of conservation of momentum states that in a closed system, the total momentum of the system remains constant, meaning that momentum cannot be created or destroyed. It can only be transferred between objects through collisions or interactions.

## 2. How is momentum calculated?

Momentum is calculated by multiplying an object's mass by its velocity. The formula for momentum is p = m x v, where p is momentum, m is mass, and v is velocity. The units for momentum are kg*m/s.

## 3. What is the difference between elastic and inelastic collisions?

In an elastic collision, both momentum and kinetic energy are conserved. This means that the total momentum and total kinetic energy of the objects before and after the collision are equal. In an inelastic collision, only momentum is conserved. Some kinetic energy is lost, typically in the form of heat or sound.

## 4. Can momentum be negative?

Yes, momentum can be negative. Momentum is a vector quantity, meaning it has both magnitude and direction. A negative momentum indicates that the object is moving in the opposite direction of the reference frame. For example, a car moving west with a momentum of -500 kg*m/s would indicate that the car is moving in the opposite direction of a reference frame that is moving east.

## 5. How does conservation of energy relate to conservation of momentum?

Conservation of energy and conservation of momentum are closely related. In a closed system, both principles must be satisfied. This means that not only is the total momentum of the system constant, but the total energy of the system (including kinetic, potential, and thermal energy) must also remain constant. This is known as the law of conservation of energy.

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