collisons and energy

[penton]

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Hi
I have been stuck on this problem for a while so i was wondering if anyone could suggest what i might be doing wrong. The question states,
" Two baseballs undergo a head on collision. Ball 1 is twice as heavy as Ball 2. Ball 1 was traveling at an initial speed of v1, while ball 2 had an initial speed of v2. the type of collision was elastic. if ball 1 travels at a speed of 7/5 v1 after impact, what is the speed of ball 2?

The way i set up the question was
m1v1+ m2(-v2) = m1(-v1f) +m2v2 ; but i get 4.8 v1=2v2 as my answer but the answer is 1.6 v1= 2v2 .

Thank you!!!!

 

[BenzylAcetate]

You have two variables, the final velocity of ball 2 and the initial velocity of ball 2, so you need two equations. This is an elastic collision so what else, besides momentum, is conserved?

 

[midnight0il]

42

 

[penton]

the kinetic energy is conserved as well.

 

[Mt Kilimanjaro]

If they're both baseballs, how is one 2x heavier than the other?

 

[moisne]

Would answer it if I were paid, but too lazy to figure it out at 4 am ...

 

[theseeker4]

If they're both baseballs, how is one 2x heavier than the other?

Very poor quality control? Either that or someone corked a baseball instead of the bat.....

 

[Psai]

e = 1/2 mv^2

 

[WhippleWhileWeWork]

If they're both baseballs, how is one 2x heavier than the other?

Waterlogged

 

[Ismet]

Closing thread. SDN is not for homework help.