2 dimensional elastic collision

  • Thread starter teleport
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  • #1
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Hey, I'm having problems with this:

A particle m with initial speed V1 collides with a particle at rest with mass 3m. After collision, particle with mass m is seen moving 30 degrees from its initial direction. What is the angle of motion of the 2nd particle after collision?

I can get three equations from momentum and energy for three unknowns but I can't solve it. Help?
 

Answers and Replies

  • #2
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Show me your equations.
 
  • #3
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x-component:

V1 = v1cos30 + 3VcosC


y-component:

v1sin30 = 3VsinC


Energy:

V1^2 = v1^2 + 3V^2,

where C is the unknown angle, v1, V are the final velocities of the m and 3m masses.
 
  • #4
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That's not exactly how I'd go about it. oops nevermind lol.
 
  • #5
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Well you see your equation 1 gives you what V1 is. So you can plug that into equation 3. Now you are only left with 2 uknowns, V and C. Now equation 2 gives you a way of getting rid of V. So now you only have 1 equation and 1 unknown, C.

btw, conservation of momentun does not use angles.

I should say conservation of momentum does not have to use angles. So if it helps, go ahead and use the total conservation of momentum equation.
 
Last edited:
  • #6
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that's wrong. Ill explain tomorrow why. Anyways thax.
 
  • #7
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Your equation in the y direction needs a negative sign.

Also, you will use angles.
 
  • #8
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Please can someone actually help?
 
  • #9
vanesch
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Please can someone actually help?

Your equations seem correct (C will then be a negative angle). What's your problem in solving them ?

You need to solve for the quantities v1, V and C and you have 3 equations.

Try to eliminate v1 and V using the first two equations to write everything as a function of C in the third one, and you'll have an equation for your angle C.
 

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