Register to reply

Particle speed relativity question

by Artichoke
Tags: particle, relativity
Share this thread:
Jan28-13, 03:14 PM
P: 1
Two protons are moving away from each other. In the frame of each proton, the other proton has a speed of .555c.[In the rest frame of the earth the protons are moving in the opposite directions with equal values of speed. What does an observer in the rest frame of the earth measure for the speed of each proton?
Enter your answers numerically separated by a comma

I thought I would just divide by 2.... clearly it is wrong. The answer is .303c, after failing many tries on mastering physics.
I want to know how you do this problem. Thank you.
Phys.Org News Partner Science news on
Scientists discover RNA modifications in some unexpected places
Scientists discover tropical tree microbiome in Panama
'Squid skin' metamaterials project yields vivid color display
Jan28-13, 04:06 PM
P: 1,100
Your problem is that you assumed "Galilean Relativity" where velocities add directly. For higher speeds this line of thinking fails. Velocities dont add directly, they add in a weird way. You should have some formula for this in your notes or text, something along the line of "velocity addition".

A key thing to realize here is that since we have high speed objects we cannot add velocities directly. Intuitively we think that velocities add directly and this is confirmed by our experience with "slow" objects (slow being up to jet speed and beyond...). But when you have higher speed objects you need to stop trusting your intuition and look at the theory, the theory of relativity.

So one thing you want to ask yourself whenever you see problems like this, ask "Is this relativistic?". If not, proceed with your intuitively understood kinematic equations. If it is relativistic you need to consider the equations of relativity.
Jan28-13, 04:09 PM
P: 616
You start by writing down the equation for transforming velocities.

Register to reply

Related Discussions
Question of Relativity and the Speed of Light? Special & General Relativity 3
Question about the speed of light and relativity Special & General Relativity 4
Newton's Third Law, Speed of Light, and Relativity question Special & General Relativity 14
Question: Particle speed & c High Energy, Nuclear, Particle Physics 3
Speed of light and particle model word question Introductory Physics Homework 0