# Need help with two questions - velocity and momentum?

1. Jun 27, 2017

### Renue

1. The problem statement, all variables and given/known data
Q1. A ball is rolling on a flat surface and another ball rolling on an inclined surface. When do both the balls have same velocity?
Q2. When two people throw a ball and catch for a period of time, will the distance between them increase, decrease, or remain the same?

2. Relevant equations
Q1. No equations or numbers given - just t1, t2, etc.
Q2. This is also a conceptual question and no equations or numbers given.

3. The attempt at a solution
Q1. I looked at the space between each ball as it is rolling, wherever the gap was same, I chose that time period as having same velocity.
Q2. The distance would remain the same if the velocity is constant throughout.
Please let me know if my thinking is in the right direction for both these questions. Thanks.

2. Jun 27, 2017

### Orodruin

Staff Emeritus
What is the difference between speed and velocity?

Q2 is unclear.

3. Jun 27, 2017

### Renue

Speed does not have direction (scalar) and velocity is a vector quantity. How do I use this to solve Q1?

I'm sorry for being unclear on Q2, as I am also unclear as to what the question is asking. All I know is - two people are playing throw and catch with a ball for sometime (no time given, no velocity given). Would the distance between these two players, increase, decrease, or remain the same. I'm still confused:-(

4. Jun 27, 2017

### haruspex

Same as what? Do you mean when the gap is at a minimum or maximum?
This is possibly ambiguous. It might mean down an inclined surface, or it really might be allowing any direction.
Is that the exact wording? Is it a translation?
it changes the requirement. If the velocity is to be the same then both the speed and direction (in three dimensions) must be the same.

Last edited: Jun 27, 2017
5. Jun 27, 2017

### phinds

I cannot see how this is a scientific question in the absence of any other information.

6. Jun 27, 2017

### haruspex

Here's a guess: someone forgot to mention that they are standing on frictionless ice, perhaps?

7. Jun 28, 2017

### Kaura

Question 2 is a bit vague as it depends on whether static friction is present.

However, if friction is not present then try to think about the change experienced by the persons when catching the ball as well as throwing the ball.

8. Jun 28, 2017

### Orodruin

Staff Emeritus
Even if friction is not present it is a vague question - it does not give you the initial condition nor any qualifier for what "some time" means.