A proton of mass 1.67 X 10(to the power of -27) travelling at a speed of 6.8 X 10(to the power of 7) m/s hits a stationary unknown particle. The proton bounces back at a speed of 4.2 X 10(to the power of 6) m/s and the particle is projected forward at a speed of 2.6 X 10(to the power of 6) m/s. Calculate the mass of the unknown particle.
Thanks!