Momentum and angles problem

[thenewbosco]

I had made an error on my previous post so i will take it back to the beginning. I can't get this one for some reason.

First look at the diagram: http://bosco.iwarp.com/diagram.jpg

OK here's the problem:

Two identical balls (mass m) undergo a collision. Initially one ball is stationary, the other has kinetic energy of 8J. The collision is partially inelastic with 2 J energy converted to heat. What is the maximum deflection angle (alpha or beta) at which one of the balls is observed?

I have come up with the following relationships using conservation of momentum and energy:

1. Vo = V1 cos a + V2 cos B

2. 0 = V1 sin a - V2 sin B

and 12 = m (V1f^2 + V2f^2) which i believe can be written

3. 0.75Vo = V1^2+V2^2

by rearranging initial kinetic energy of ball one to solve for m.

How do i go about comparing alpha and beta? Are my equations correct
Help please! thanks

[Andrew Mason]

I have come up with the following relationships using conservation of momentum and energy:

1. Vo = V1f cos a + V2f cos B

2. 0 = V1f sin a + V2f sin B

and 12 = m (V1f^2 + V2f^2) which i believe can be written

3. 0.75Vo = V1f^2+V2f^2

1. and 2. are fine. 3. should have Vo^2:

This is not a trivial problem to solve. Use 1 and 2. to find cos\beta \text{ in terms of } sin\alpha \text{ and } cos\alpha

Then look at the ranges of values that cos\beta can have. There should be a \sqrt{.75} term in there somewhere.

AM

[thenewbosco]

Well i have attempted this another way and have got the following:

2 = mv_{1}v_{2} (cos \alpha }+ \beta)

now i do not know how to compare \alpha and \beta

any help

[thenewbosco]

??????????

[Andrew Mason]

Well i have attempted this another way and have got the following:

2 = mv_{1}v_{2} (cos \alpha }+ \beta)

now i do not know how to compare \alpha and \beta

any help
It has to have \beta in terms of \alpha ONLY. You can do this with these equations: determine v2f in terms of v1f using 2. and substitute into 1. to find v1f in terms of \alpha \text{ and } \beta. Substitute also into 3. to find v1f. (v_0^2 = 16/m). Then combine the two to find beta in terms of \alpha (the m falls out).

AM

[thenewbosco]

I dont know why this is not working out but after trying what you said i got:

[tex] 3sin^2\beta (cos^2\alpha + 2cos\alpha + cos^2\beta) = 4(sin^2\beta+sin^2\alpha)[/itex]

It should probably be simpler shouldnt it?

I really want to get this one done but it just isnt working out
Thanks for all your help on this one

[thenewbosco]

???????????

[Andrew Mason]

I dont know why this is not working out but after trying what you said i got:

[tex] 3sin^2\beta (cos^2\alpha + 2cos\alpha + cos^2\beta) = 4(sin^2\beta+sin^2\alpha)[/itex]

It should probably be simpler shouldnt it?

I really want to get this one done but it just isnt working out
Thanks for all your help on this one
I told you it was non-trivial. Have a look at the solution for an elastic collision at: http://rustam.uwp.edu/201/L12/lec12_w.html (scroll down to the collision in 2 dimensions). For elastic collisions the two angles add to 90 degrees. The question is asking how the sum of the two angles in an inelastic collision where 25% of the energy is lost compares to 90 degrees.

AM