Help Me Understand the Velocities and Collisions of Three Identical .5 lb Balls

  • Thread starter prdoring
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In summary, a ball weighing .5 lbs travels a vertical distance 3 feet downward before changing direction to travel on a horizontal path. Shortly thereafter, it strikes another ball (of same weight) which then travels some distance before striking another identical ball. After the second collision, the first ball, the one that started from rest, has a velocity of 3 feet/second, the second ball has a velocity of 2.75 feet/second, and the third ball has a velocity of .85 feet/second.
  • #1
prdoring
3
0
First off i need to make the diclaimer that this is not for any homework or any assignment of any type... i just need to know the answer, and I am not a psyics guy... so please help me out here


A ball weighing .5 lbs travels a vertical distance 3 feet downward before changing direction to travel on a horizontal path. Shortly thereafter, it strikes another ball (of same weight) which then travels some distance before striking another identical ball. What are the velocities of the three balls after the second collision? Is there a third collision? You may neglect friction and consider the balls as particles. The coefficient of restitution between all three balls is .85.
 
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  • #2
Sure looks like homework to me, and definitely doesn't belong in the general forums. Thread moved to Homework Help, Intro Physics.

prdoring, we do not do your work for you here on the PF. Where did this question come from? If you're not a physics guy, why do you need to figure this out? Who is telling you that "you may neglect friction and consider the balls as particles"? Sounds pretty didactic to me.

BTW, you did not give enough information to solve the problem anyway.
 
  • #3
berkeman said:
Sure looks like homework to me, and definitely doesn't belong in the general forums. Thread moved to Homework Help, Intro Physics.

prdoring, we do not do your work for you here on the PF. Where did this question come from? If you're not a physics guy, why do you need to figure this out? Who is telling you that "you may neglect friction and consider the balls as particles"? Sounds pretty didactic to me.

BTW, you did not give enough information to solve the problem anyway.


not sure what the question is about... to tell the truth its part of this game me and my friend are playing... sortof a pseudo scavenger hunt... we send each other rediculous questions... and we have to use all available resources to find the answers...
 
  • #4
prdoring said:
not sure what the question is about... to tell the truth its part of this game me and my friend are playing... sortof a pseudo scavenger hunt... we send each other rediculous questions... and we have to use all available resources to find the answers...

Fair enough. But the question is too much like homework/coursework for us to let it sit in the general technical forums, and Homework Help rules still have to apply. It's too easy for students to use the PF for cheating, without the Rules that we have in place for the Homework Help forums.

So all I can do is offer you a couple hints and pointers to information that you can use to solve the question yourself. First, you would need to know whether the ball was released from rest, or had some initial velocity (that's the main thing that's missing in the question). Second, you would use the kinematic equations of motion (the ones for constant acceleration due to gravity) to tell you the velocity of the ball right when it got to the floor and hit something at an angle to change to sideways velocity:

http://en.wikipedia.org/wiki/Kinematics

Then you would use something like conservation of momentum to get to the final velocities of the balls after the collisions

http://en.wikipedia.org/wiki/Conservation_of_momentum#Conservation_of_momentum
 
  • #5
still completely lost man... atleast throw some formulas my way
 

1. How does the velocity of a ball affect its collision with another ball?

When two balls collide, their velocities are important factors in determining the outcome of the collision. The velocity of a ball is its speed and direction of motion. If two balls have different velocities, they will collide at an angle and transfer some of their energy and momentum to each other. If two balls have the same velocity, they will collide head-on and transfer all of their energy and momentum to each other.

2. What is the difference between elastic and inelastic collisions?

In an elastic collision, the total kinetic energy of the system remains constant before and after the collision. This means that the balls bounce off each other without losing any energy. In an inelastic collision, some of the kinetic energy is lost during the collision, usually in the form of heat or sound. This means that the balls will not bounce off each other with the same speed as before the collision.

3. How does the mass of a ball affect its collision with another ball?

The mass of a ball is an important factor in collisions. In a head-on collision between two balls with different masses, the ball with the greater mass will transfer more of its energy and momentum to the other ball. This is because it has more inertia and is harder to move. In a glancing collision, the mass of the balls will also affect the angle at which they bounce off each other.

4. Can three identical balls have different velocities in the same system?

Yes, three identical balls can have different velocities in the same system. This is because the velocity of a ball is affected by its initial speed and direction, as well as any external forces acting on it. If one ball is given an initial velocity or experiences a force, it may have a different velocity than the other two balls in the system.

5. How do you calculate the final velocities of three identical balls after a collision?

The final velocities of three identical balls after a collision can be calculated using the conservation of momentum and the conservation of kinetic energy equations. The total momentum and kinetic energy of the system before the collision must be equal to the total momentum and kinetic energy after the collision. By solving these equations, you can determine the final velocities of the balls after the collision.

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