What Are the Directions of Impulse and Momentum in Collisions?

[whitehorsey]

1. A particle is initially traveling to the right when it hits a wall and turns around to the left. The momentum after the collision is less than the initial momentum.
a)impulse on the particle is to the left
b)impulse on the particle is to the right
c)no impulse on the particle
d)none

When a particle hits the floor and comes to rest, what is the direction of the total impulse?

3. For the first problem, the question states that the momentum is less after the collision. I thought the momentum before = momentum after. Does it have something to do with impulse?

The second question is the direction of the impulse up because of Newton's Second Law and impulse is a force?

 

[cepheid]

1. A particle is initially traveling to the right when it hits a wall and turns around to the left. The momentum after the collision is less than the initial momentum.
a)impulse on the particle is to the left
b)impulse on the particle is to the right
c)no impulse on the particle
d)none

When a particle hits the floor and comes to rest, what is the direction of the total impulse?

3. For the first problem, the question states that the momentum is less after the collision. I thought the momentum before = momentum after. Does it have something to do with impulse?

Hi whitehorsey,

The momentum of the ball does not have to be conserved, because momentum is only conserved for systems on which NO external forces act. If you consider just the ball to be your system, it has an external force acting on it. Namely: the force from the wall. So, its momentum can change.

As far as actually answering the question, answer this question first: what is the relationship between impulse and momentum? That will tell you absolutely everything you need to know.

The second question is the direction of the impulse up because of Newton's Second Law and impulse is a force?

No, impulse is not the same thing as force. They are two different physical quantities. Again, you need to look up the definition of impulse (and its relationship to momentum) in your book or notes.

 

[whitehorsey]

Hi whitehorsey,

The momentum of the ball does not have to be conserved, because momentum is only conserved for systems on which NO external forces act. If you consider just the ball to be your system, it has an external force acting on it. Namely: the force from the wall. So, its momentum can change.

As far as actually answering the question, answer this question first: what is the relationship between impulse and momentum? That will tell you absolutely everything you need to know.

No, impulse is not the same thing as force. They are two different physical quantities. Again, you need to look up the definition of impulse (and its relationship to momentum) in your book or notes.

Is it impulse = change in momentum? So for the first one impulse on the particle is to the left because momentum changed direction. As for the second one, I'm thinking its down now because the direction didn't change and the ball didn't bounce back up.

 

[cepheid]

Yes, the impulse is equal to the change in momentum.

For the first problem: you are correct.

For the second problem: what was the momentum initially? What about finally? So, what is the difference between these two and which way does that vector (the difference) point?

 

[Nickie]

I would like to clarify and provide a response to the questions regarding momentum and impulse.

1. The correct answer is a) impulse on the particle is to the left. This is because impulse is defined as the change in momentum, and since the particle's momentum has decreased, the impulse must be in the opposite direction to the initial momentum.

2. When a particle hits the floor and comes to rest, the direction of the total impulse is downwards. This is because the floor exerts an upward force on the particle to bring it to rest, and according to Newton's Third Law, there must be an equal and opposite force acting on the floor. This force is the total impulse acting in the downward direction.

3. The statement "momentum before = momentum after" is only true in a closed system with no external forces acting on it. In this problem, the particle experiences an external force from the wall, causing a change in its momentum. This change in momentum is known as impulse.

In regards to the direction of the impulse, it is not always in the same direction as the force. Impulse is the product of force and time, and can act in any direction depending on the direction and duration of the force applied. In this case, the impulse is in the opposite direction to the force applied by the wall, causing the particle to change its direction. This is an important concept in understanding collisions and the conservation of momentum.

Overall, momentum and impulse are related concepts that help us understand the motion of objects and the effects of forces on them. It is important to understand the direction and magnitude of these quantities in order to accurately analyze and predict the behavior of physical systems.