- #1

- 83

- 1

I know that when m> m1 , angle <90'

when m<m1 , angle >90'

but there is no mathematical proof to show this result...

...

does anyone help me solve this problem?

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- Thread starter mysqlpress
- Start date

- #1

- 83

- 1

I know that when m> m1 , angle <90'

when m<m1 , angle >90'

but there is no mathematical proof to show this result...

...

does anyone help me solve this problem?

- #2

Mentor

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Can you prove the first result? (For equal masses.)

- #3

- 83

- 1

mv=m1v1cosx+mv2cosy- (1)

v=v1cosx+v2cosy

0=m1v1sinx-mv2siny - (2)

0=v1sinx-v2siny

(1)^2+(2)^2

v^2 = (v1)^2+(v2)^2 +2v1v(cosxcosy-sinysinx)

KE conserved

mv^2 =m1v1^2+mv2^2

v^2=v1^2+v2^2

cos(x+y) = 90'

- #4

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- #5

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Thanks ! I've proven that. :)

- #6

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- #7

- 4

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mv=m1v1cosx+mv2cosy- (1)

v=v1cosx+v2cosy

0=m1v1sinx-mv2siny - (2)

0=v1sinx-v2siny

(1)^2+(2)^2

v^2 = (v1)^2+(v2)^2 +2v1v(cosxcosy-sinysinx)

KE conserved

mv^2 =m1v1^2+mv2^2

v^2=v1^2+v2^2

cos(x+y) = 90'

I understand everything except what is in bold. First, you are finding the momentum along the X. Then finding the momentum along the Y. Then somehow combine them in the equation for the conservation of energy. I have all of that already, but I don't understand the combining itself and don't understand the bolded areas

- #8

- 4

- 0

Ø1 + ø2 = 90,

so it is safe to assume that :

cos(Ø1 + ø2) = 0

since cos(90) = 0. Now, for the actual proof, start by using the formula for conservation of kinetic energy:

K1i + K2i = K1f + K2f.

After simplifying, you will get:

V1i^2 = V1f^2 + V2f^2.

According to law of cosines,

c^2 = a^2 + b^2 -2(ab)cosC.

CosC is The same value as cos(ø1 + ø2), so

c^2 = a^2 + b^2 -2(ab)cos

- #9

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Good! (Sorry I didn't have time to respond earlier.)NvM. I got it. Law of cosines and sum difference formulas.

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