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

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The discussion revolves around a physics question involving the velocities and collisions of three identical 0.5 lb balls, where one ball drops and collides with another. Participants express skepticism about the legitimacy of the query, suspecting it resembles homework, and emphasize the need for more information to solve the problem, such as the initial conditions of the balls. They suggest using kinematic equations and conservation of momentum to derive the final velocities after the collisions. The conversation highlights the importance of adhering to forum rules regarding homework help, as it could facilitate academic dishonesty. Overall, the inquiry remains unresolved due to insufficient details and the forum's guidelines.
prdoring
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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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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.
 
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...
 
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
 
still completely lost man... atleast throw some formulas my way
 
Thread 'Variable mass system : water sprayed into a moving container'

Thread 'Variable mass system : water sprayed into a moving container'

Starting with the mass considerations #m(t)# is mass of water #M_{c}# mass of container and #M(t)# mass of total system $$M(t) = M_{C} + m(t)$$ $$\Rightarrow \frac{dM(t)}{dt} = \frac{dm(t)}{dt}$$ $$P_i = Mv + u \, dm$$ $$P_f = (M + dm)(v + dv)$$ $$\Delta P = M \, dv + (v - u) \, dm$$ $$F = \frac{dP}{dt} = M \frac{dv}{dt} + (v - u) \frac{dm}{dt}$$ $$F = u \frac{dm}{dt} = \rho A u^2$$ from conservation of momentum , the cannon recoils with the same force which it applies. $$\quad \frac{dm}{dt}...
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