# Momentum of a Fast-Moving Proton

1. Aug 28, 2014

### vanceEE

How was the magnitude of the velocity vector found in the example provided? This is a particle in space so I has 3 coordinates but I am told that the velocity vector is m/s, so wouldn't the magnitude just be 2*10^7 m/s?

2. Aug 28, 2014

### vanceEE

3. Aug 28, 2014

### HallsofIvy

Staff Emeritus
Certainly the units of speed or velocity is "m/s" but I see no "example provided".

4. Aug 28, 2014

### vanceEE

Just posted it, must be a misprint because three components of the vector would need to be included whether zero or not, so according to the solution, I believe that the author meant that the velocity vector was <2*10^7, 1*10^7, -3*10^7>m/s

5. Aug 28, 2014

### Staff: Mentor

The calculation of the momentum $\vec p$ includes the three vector components of velocity as you gave them, so the author must have accidentally given only one of them in the initial problem statement, and nobody caught it during proof-reading.