An unstable particle is at rest and suddenly decays into two fragments. No external forces act on the particle or its fragments. One of the fragments has a speed of 0.76c and a mass of 6.68×10?27kg, while the other has a mass of 1.67×10?27kg.
What is the speed of the less massive fragment?
The momentum of lighter particle in rest frame of reference
p1 = m1v1 / sqrt(1 - v1^2 / c^2)
The momentum of heavier particle in rest frame of reference
p2 = m2v2 / sqrt(1 - v2^2 / c^2)
p1 = p2
m1v1 / sqrt(1 - v1^2 / c^2) = m2v2 / sqrt(1 - v2^2 / c^2)
v1^2 / (1 - v1^2 / c^2) = (m2/m1)^2 x v2^2 / (1 - v2^2 / c^2)
v1^2 / (1 - v1^2 / c^2) = (6.68 x 10^-27 / 1.67 x 10^-27)^2
v1^2 = 21.88*c^2(1 - v1^2/c^2)
v1^2 = 21.88*c^2 - 21.88*v1^2
22.88*v1^2 = 21.88*c^2
v1^2 = 21.88*c^2 / 22.88
v1 = 0.978*c
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