Lecture16

# Lecture16 - Physics 344 Foundations of 21 st Century...

This preview shows pages 1–5. Sign up to view the full content.

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Physics 344 Foundations of 21 st Century Physics: Relativistic and Quantum Systems Instructor: Dr. Mark Haugan Office: PHYS 282 [email protected] TA: Dan Hartzler Office: PHYS 7 [email protected] Grader: Fan Chen Office: PHYS 222 [email protected] Office Hours: If you have questions, just email us to make an appointment. We enjoy talking about physics! Help Session: Thursdays 2:00 – 4:00 in PHYS 154 Reading: Review Lecture Slides and Text Exam 1: Wednesday, October 5 at 8:00pm in WTHR 104 x t A B Clocks move along the worldlines shown and are used to measure the time that elapses between events A and B. Question 1: The clock(s) following which worldline(s) measure the spacetime interval between A and B? A) B) C) D) and E) none of them Question 2: The clock(s) following which worldline(s) measure the longest time interval between A and B? A) B) C) D) and E) none of them Question 3: The clock(s) following which worldline(s) measure the shortest time interval between A and B? A) B) C) D) and E) none of them synchronized * * * Question 4: A spaceship leaves Earth (event A) travels to a star 8 light-years away and then returns (event B) 20 yrs later. How much time elapses between events A and B as measured by the ship’s clock? Assume that the ship accelerates for a very short period of time while reversing course near the star so that it spends almost the entire trip traveling at constant speed. A) 20 yrs B) 16 yrs C) 12 yrs D) 10 yrs D) 8 yrs What are the Earth-frame components of the ship’s 4-velocity on the outward trip? x = 8 yrs t = 20 yrs Neglecting contributions from the short periods of accelerated motion, the outbound time lapse is approximately the interval between departure and turn-around, 2 2 100 64 6 out out out t x yr yr τ ∆ ≈ ∆- ∆ =- = * ˆ ˆ ˆ ˆ ˆ ˆ ( / ) ( / ) (10 / 6) (8/ 6) (5/ 3) (4 / 3) out out out out out u t t x x t x t x τ τ ⇒ = ∆ ∆ + ∆ ∆ = + = + The trip back takes the same amount of time. Question 5. Two photons of energy E are traveling away from each other in opposite directions. What is the mass of this 2-photon system? A) 0 B) E/2 C) E D) 2E 2 2 = 4 2 sys sys sys sys E E E E E P M P P E E ⇒ ⇒ ⇒ - + ⇒ = ⋅ =- = ≐ * The mass of any system is its rest energy, its energy measured in a frame in which the system’s momentum is zero....
View Full Document

## This note was uploaded on 12/09/2011 for the course PHYS 344 taught by Professor Garfinkel during the Fall '08 term at Purdue.

### Page1 / 12

Lecture16 - Physics 344 Foundations of 21 st Century...

This preview shows document pages 1 - 5. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online