Question

Relativity Problem 8:
In several examples in this section of the course, we have spoken about rockets or trains traveling at significant fractions of the speed of light. If electrical energy costs around $0.06 per 106 J, what would it cost to accelerate an electric train with a mass of about 100,000 kg to a speed of 3 ? ? 5

Relativity Problem 9:
Suppose that somewhere in deep space a rock with mass ?1 = 12 kg is moving in the +? direction with ?1,? = + 4 ? in some inertial reference frame. This rock then strikes another rock 5 of mass ?2 = 28 kg at rest (?2,? = 0). Pretend that the first rock, instead of instantly vaporizing into a cloud of gas (as any real rocks colliding at this speed would), simply bounces off the more massive rock and is subsequently observed to have an ?-velocity ?1,? = −5/13. What is the larger rock’s ?-velocity ?2,? after the collision? [hint: use conservation of (relativistic!) momentum].

Answer 1