# Pi - mesons question

1. Apr 15, 2004

### EIRE2003

A beam of charged pi-mesons is travelling with a speed of v=0.3c.
The mean life of a pi-meson is 2.6 x 10^-8s. What is the mean distance travelled by a pi meson before it decays?

How do u do this???

2. Apr 15, 2004

### chroot

Staff Emeritus
Do you understand how to calculate time dilation?

- Warren

3. Apr 15, 2004

### EIRE2003

No

4. Apr 15, 2004

### chroot

Staff Emeritus
Have you not been paying attention in class or something?

- Warren

5. Apr 15, 2004

### EIRE2003

Im not in school i finished last yr. Im repeating cause our teacher was never in to teach us the stuff. So im trying to learn this stuff myself from the past examination papers. My leaving cert is in june.

6. Apr 15, 2004

### chroot

Staff Emeritus
Well, in special relativity theory, when an object is moving at velocity v with respect to a stationary observer, the object will appear to suffer a time dilation of

$$T = \frac{T_0}{\sqrt{1 - v^2/c^2}}$$

where $T$ is the time measured by the observer and $T_0$ is the time as measured in the rest frame of the pion.

In other words, the pion will seem to live longer when moving than it would when at rest by a factor of $1/\sqrt{1 - v^2/c^2}$.

Does this make sense?

- Warren

7. Apr 15, 2004

### EIRE2003

not really. ive seen this in hawkings book universe in a nutshell but never understood it.

I dont understand what T_o is?

Maybe if u cud actually do the sum and i will go through it and try to get my head around it. Then it wont be as confusing. I just need an example of how its done.

8. Apr 15, 2004

### chroot

Staff Emeritus
$T_0$ is the proper time, the time experienced by the pion itself. Plug in its lifetime here.