Cosmology and Quantum Introduction homework

Cosmology and Quantum Introduction homework - PHYSICS 6...

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PHYSICS 6 SPRING 2006 HOMEWORK 3 (due Tues. Feb.21) Read : Finish reading the Lightman selection on relativity. Read Feynman, Chapters 1 (to reacquaint yourselves with the atomic/molecular theory of matter) & 4 (read this carefully; energy is fundamental to all we will discuss after E=mc 2 ). Problems: (Problems are to be handed in at the due date.) 1. The charged pion ( π + ) decays into other particles. It has an average decay time of 2.6x10 -8 sec. a. If a π + is travelling in a lab at 0.9999c what is its average decay time? b. How far does it travel before decaying (on the average)? c. The π + turns into three particles (usually muon and 2 neutrinos) when it decays. Suppose the muon is produced along the direction of the π + motion and has a velocity of 0.99c in the π + rest frame. What is the muon velocity in the lab? 2. Judy and Andy are twins. Judy gets on a rocket that goes to a star system 20 light years away from earth (as measured from earth, i.e. Andy's frame of reference). a. She travels at 0.8c. How many years does it take her to reach the star according to
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