*D-3He fusion. Professor Heidbrink studies fusion reactions between deu-terium (a hydrogen isotope with twice the proton mass) and 3He (a helium isotope with three times the proton mass).1 Since positively charged nuclei repel each other, fusion reactions only occur when the relative velocity of the nuclei is very large, large enough that the nuclei get close enough for the strong nuclear force to take over. In an experiment in the DIII-D toka-mak, Professor Heidbrink hopes to achieve this by injecting an 80 keV 3He beam into a plasma with relatively cold deuterium ions. Consider a collision between a 3He ion with velocity vHe and a stationary deuteron. (a) What is the center-of-mass velocity? (b) What are the 3He and deuteron velocities in the CM frame? [Hint: vHe c.] (c) What is the reduced mass for this two-body problem?