ExamIIIandIIIbGJSolutions

# ExamIIIandIIIbGJSolutions - Thursday,November19,2009...

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1. [25 pts] In the earth’s reference frame, a tree is at the origin and a pole is at x=50km. Lightning strikes both the tree and the pole at t=5 sec. The same lightning strikes are observed by a rocket traveling in the +x-direction at 0.9c. Note that the origins of the two reference frames (earth and rocket) coincide at time t=0 in both reference frames. NAME / Section #: ___________________________________ / _______ Exam III Problem #1 Phys270 (a) [15 pts] What are the space-time coordinates for these two events in the rocket’s reference frame? (b) [5 pts] In the rocket’s frame, which event occurs first and how much time elapses between the two events? (c) [5 pts] What is the distance between the two events in the rocket’s reference frame? 2. [25 pts] A planet is 500 light years away from earth as measured in the earth’s reference frame. An astronaut makes the one-way trip in 20 years as measured in the rocket’s frame. The rocket has a rest mass of 10,000 kg. Assume the rocket quickly accelerates and decelerates so that the time required to do so may be ignored. NAME / Section #: ___________________________________ / _______ Exam III Problem #2 Phys270 (a) [9 pts] How fast is the rocket moving as measured in earth’s reference frame? (b) [8 pts] How long does the trip take as measured by people in the earth’s reference frame? (c) [8 pts] How much energy is required to accelerate the rocket to this speed (as found in part a)? 3. [25 pts] Two rockets, A and B, approach the earth from opposite directions at speed 0.8c. The length of each rocket measured in its rest frame is 200 m. NAME / Section #:

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ExamIIIandIIIbGJSolutions - Thursday,November19,2009...

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