• Got a question on how to use our new website? Check out our user guide here!

Question on Special Relativity (1 Viewer)

Vizsla

Member
Joined
Dec 18, 2014
Messages
45
Location
Sydney
Gender
Male
HSC
2015
11733299_1093049944056239_928504696_n.jpg

Could one of you please help me with this question and explain how the two answers differ.
 

rand_althor

Active Member
Joined
May 16, 2015
Messages
554
Gender
Male
HSC
2015
a) An observer on Earth would see the rocket travel the normal distance, in a dilated time period. You would calculate the time taken to complete the journey using v=d/t. And then use the time dilation formula to calculate the dilated time.

b) An astronaut on the rocket would see the path of the rocket to be contracted, and would record the time taken to be normal. You would calculate the contracted length, and then use v=d/t to determine the time taken.
 

porcupinetree

not actually a porcupine
Joined
Dec 12, 2014
Messages
663
Gender
Male
HSC
2015
View attachment 32207

Could one of you please help me with this question and explain how the two answers differ.
The times should be equal. However, if we were hypothetically talking about someone on earth observing the rocket, or vice versa, time would appear to run slower in the observed frame of reference
 

MaccaFacta

New Member
Joined
Aug 7, 2007
Messages
28
Gender
Male
HSC
N/A
This is a lot more complicated that it looks... a rocket travelling at 0.75 c will take 9 / 0.75 = 12 years to travel the distance. But let's pretend that someone on the "distant planet" shines a green light towards Earth when the rocket arrives - then that signal would take 9 years to get from there to here. So the observer on Earth would wait 21 years for confirmation that the rocket had arrived! An astronaut in the rocket will observe length contraction of the distance between Earth and the distant planet, so the distance from Earth to the distant planet in the astronaut's reference frame is 5.95 light years. So the trip will take 7.93 years from the astronaut's reference frame.
 

PhysicsMaths

Active Member
Joined
Dec 9, 2014
Messages
179
Gender
Male
HSC
2015
This is a lot more complicated that it looks... a rocket travelling at 0.75 c will take 9 / 0.75 = 12 years to travel the distance. But let's pretend that someone on the "distant planet" shines a green light towards Earth when the rocket arrives - then that signal would take 9 years to get from there to here. So the observer on Earth would wait 21 years for confirmation that the rocket had arrived! An astronaut in the rocket will observe length contraction of the distance between Earth and the distant planet, so the distance from Earth to the distant planet in the astronaut's reference frame is 5.95 light years. So the trip will take 7.93 years from the astronaut's reference frame.
Your answer is correct but it seems you're over complicating things a bit
All that's required is substituting 12 into the time dilation equation
 

Users Who Are Viewing This Thread (Users: 0, Guests: 1)

Top