# Electrons - Relativistic velocity addition

charmedbeauty

## Homework Statement

an observer measures the velocity of two electrons, finding one with a speed c/2 in the x direction and the other c/2 in the y direction. what is the relative speed of the two electrons.

## The Attempt at a Solution

Im not sure if this is right it seemed to easy.

but suppose that electron 1 is called b and the other a

then v(b)= √(c2/4+c2/4)
since they are at right angles to each other. is this right?

voko

The velocities are very high, you need to use special relativity here.

Gold Member
2022 Award

## Homework Statement

an observer measures the velocity of two electrons, finding one with a speed c/2 in the x direction and the other c/2 in the y direction. what is the relative speed of the two electrons.

## The Attempt at a Solution

Im not sure if this is right it seemed to easy.

but suppose that electron 1 is called b and the other a

then v(b)= √(c2/4+c2/4)
since they are at right angles to each other. is this right?

No. That is a non-relativistic velocity-addition and would give you the right answer for a speeding bullet on Earth but NOT for things traveling at relativistic speeds.

charmedbeauty

The velocities are very high, you need to use special relativity here.

No. That is a non-relativistic velocity-addition and would give you the right answer for a speeding bullet on Earth but NOT for things traveling at relativistic speeds.

oh yeah that makes sense ok cool thanks.

KingBigness

How did you go with the rest of the assignment =P