Kinetic Enrgey according to another viewer

[ori]

2 particles with mass M and Kinetic Engergy T moving toward each other.
what is the kinetic energy T' as it measured by the other particle
given data: T=...
m=...

thanks

 

[blue_sky]

Why you proposed this question?

 

[ori]

Why you proposed this question?

training for test

that's what i did, could anyone tell what's my prob here:
for first particle
T=mc^2(r-1)
since we're working with Mev , c=1
T=m(r-1)
r=T/M+1
therefore
(1) V^2=T/(T+M)
(V is speed of particle one according to "the lab")

therefore the speed of particle2 is -V (simetry)
now we use additional formula
u1=(u1'+u3)/(1+u1'u3)
whille u1 is velocity of particle1 according to the lab (u1=V)
u1' is velocity of particle 1 according to particle 2
u3 is the velocity between lab to particle2 (u3=-V)
therefore
u1'=2V/(V^2+1)

now i look on kinetic energy of particle 1 according to particle 2:
T'=m(r-1)
while r=1/sqrt(1-u1'^2)
i assigned u1' & V and got
T'=4/3M
this isn't correct..