Engineering Physics 2 Homework

# Engineering Physics 2 Homework - homework 14 KIM JI Due...

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homework 14 – KIM, JI – Due: Apr 27 2008, 4:00 am 1 Question 1, chap 36, sect 3. part 1 of 3 10 points A spaceship travels with a speed of 0 . 8 c as it passes by the Earth on its way to a distant star, as shown in the diagram below. The pilot of the spaceship measures the length of the moving ship as 30 m. 0 . 8 c Earth Determine its length as measured by a per- son on Earth. Correct answer: 18 m (tolerance ± 1 %). Explanation: Let : L 0 = 30 m and v = 0 . 8 c. Applying length contraction, L = L 0 γ = L 0 r 1 v 2 c 2 = (30 m) R 1 (0 . 8 c ) 2 c 2 = 18 m . Question 2, chap 36, sect 3. part 2 of 3 10 points The pilot of the spaceship observes that the spaceship travels for 8 years. Determine how much time has passed ac- cording to a person on Earth. Correct answer: 13 . 3333 years (tolerance ± 1 %). Explanation: Δ T = Δ T 0 γ = 8 years × 1 . 66667 = 13 . 3333 years . Question 3, chap 36, sect 3. part 3 of 3 10 points Some time after passing the Earth, the pilot shoots a laser pulse backward at a speed of 3 × 10 8 m / s with respect to the spaceship. Determine the speed of the laser pulse as measured by a person on Earth. Correct answer: 3 × 10 8 m / s (tolerance ± 1 %). Explanation: A laser pulse travels at the speed of light, in- dependent of the frame in which it is measured ( the key point of special relativity). Thus the Earth observer sees the pulse traveling at the same speed as the pilot, 3 × 10 8 m / s . Question 4, chap 36, sect 3. part 1 of 2 10 points Two Frecrackers explode at the same place in a rest frame with a time separation of 14 s in that frame. ±ind the time between explosions, as mea- sured in a frame moving with a speed 0 . 6 c with respect to the rest frame according to classical physics without the special theory of relativity. Correct answer: 14 s (tolerance ± 1 %). Explanation: According to classical physics: t = t 0 = 14 s . Question 5, chap 36, sect 3. part 2 of 2 10 points ±ind the time between explosions, as mea- sured in a frame moving with a speed 0 . 6 c with respect to the rest frame according to the special theory of relativity. Correct answer: 17 . 5 s (tolerance ± 1 %). Explanation:

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homework 14 – KIM, JI – Due: Apr 27 2008, 4:00 am 2 According to the special theory of relativ- ity: t = t 0 r 1 ( v c ) 2 = (14 s ) r 1 ( 0 . 6 c c ) 2 = 17 . 5 s . Question 6, chap 36, sect 4. part 1 of 1 10 points Rods P and Q are at rest in an inertial reference frame and oriented as shown. Both rods have length L in this reference frame. A person moves at a relativistic speed in the positive x direction. x y Q L P L O Which of the following would be the lengths, as compared to L , observed for these rods by the person? P
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Engineering Physics 2 Homework - homework 14 KIM JI Due...

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