Relativity_velocity addition and doppler effect

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SUMMARY

The forum discussion centers on a physics problem involving relativistic velocity addition and the Doppler effect, specifically in the context of the starship Enterprise NCC1701 and a Klingon warbird. The problem requires calculating the necessary velocity of the Klingon warbird to evade a proton torpedo fired at 0.75c from the Enterprise, which is traveling at 0.6c. Additionally, the discussion addresses the communication frequency of Klingon warbirds at 2.00 THz and the frequency needed for colonists on the moon of Eridani to communicate with the warbird.

PREREQUISITES
  • Understanding of relativistic velocity addition
  • Knowledge of the Doppler effect in the context of light and sound
  • Familiarity with the concept of frequency shifts due to relative motion
  • Basic principles of special relativity
NEXT STEPS
  • Study the equations for relativistic velocity addition
  • Research the Doppler effect and its application in astrophysics
  • Learn about frequency shifts in electromagnetic waves due to relative motion
  • Explore practical examples of communication frequencies in space exploration
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kkkeleven
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Homework Statement


The Enterorise NCC1701 is cruising 0.6c above the moon of Eridani when it spots a Klingon warbird sunwards.
i. It fires a proton torpedo at speed 0.75c relative to the ship at the Klingon warbird. Assuming the proton torpedo does not accelerate, at what velocity must the Klingon warbird move to evade the proton torpedo I. relative to Enterprise II. relative to the moon of Eridani.
ii. Seeing that the warbird has moved just enough to evade the proton torpedo, the Enteprise proceeds to “open hailing frequencies”. The ship’s computer scans the library and determines that Klingon warbireds communicate at frequencies of 2.00 THZ, which frequency must the Enterprise use?
iii. Just as the Enterprise is about to send the message, colonists on the moon of Eridani also wants to hail the Klingon warbird. What frequencies should they use?

Thank you very much!

Homework Equations





The Attempt at a Solution


 
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This is a bad problem

the direction of movement of the ship vs. the moon of Eridiani isn't given so you can't answer the questions about this moon.

How can the torpedo not accelerate and stil hit the Klingon ship if it tries to evade? It seems the first question is only answerable if the warbird and the enterprise and the torpedo all move only on a single line. Then you can use the equation for relativistic velocity addition.
 
kkkeleven said:

Homework Statement


The Enterorise NCC1701 is cruising 0.6c above the moon of Eridani when it spots a Klingon warbird sunwards.
i. It fires a proton torpedo at speed 0.75c relative to the ship at the Klingon warbird. Assuming the proton torpedo does not accelerate, at what velocity must the Klingon warbird move to evade the proton torpedo I. relative to Enterprise II. relative to the moon of Eridani.
ii. Seeing that the warbird has moved just enough to evade the proton torpedo, the Enteprise proceeds to “open hailing frequencies”. The ship’s computer scans the library and determines that Klingon warbireds communicate at frequencies of 2.00 THZ, which frequency must the Enterprise use?
iii. Just as the Enterprise is about to send the message, colonists on the moon of Eridani also wants to hail the Klingon warbird. What frequencies should they use?

Thank you very much!

Welcome to PF :smile:
We don't provide solutions to students, but we give hints to point you in the right direction.

Homework Equations

What equations, dealing with relativistic velocities, are you aware of?
Any equations dealing with how frequency shifts with velocity?