- #1
Jimmy87
- 686
- 17
- Homework Statement
- Part (iii)
- Relevant Equations
- conservation of momentum and conservation of kinetic energy
Part (iii) is the part I am stuck on and is a 5 mark question. I have some idea of how to attempt it shown below
momentum is conserved so mux = mvy + mvz
(where ux is the initial velocity before the collision of ball x, vy is the velocity after the collision of ball y and vz is the velocity after the collision of ball z)
They are all indentical masses so they all cancel to give ux = vy + vz
Since kinetic energy is conserved then we have:
½(mux)2 = ½(mvy)2 + ½(mvz)2
The halves and masses cancel to give:
ux2 = vy2 + vz2
Since ux = vy + vz from earlier we have:
(vy + vz)2 = vy2 + vz2 which gives:
vy2 + vz2 + 2vyvz = vy2 + vz2
2vyvz = 0
Now I am stuck as I was going to say that vy must be zero because vz isn't (it is 1.5 m/s). Then I realized the question asks to prove vz is not zero so I can't really use this assumption?
edit: I was going to go on to say that since ball y must be zero then we can go back to the original equation which is ux = vy + vz to say that ux = vz and the question tells us that ux is 1.5 m/s. However, I have had to assume vy is zero but it doesn't give me this information in the question so I can't really do that can I?
Any help is appreciated
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