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?