# Muons and Relativity

1. Jan 25, 2015

### EgpYo

1. The problem statement, all variables and given/known data
A muon has a lifetime of 2.0x10^-6 seconds when at rest, after which time it decays into other particles
a) Ignore any effects of relativity discussed in this section. If the muon was moving at 0.99c, how far would it travel before decaying into other particles, according to Newtonian mechanics?
b) How long would the muon last, according to an observer in earths frame of reference?
c)How far would the muon actually travel, when viewed moving at 0.99c?
d) Compare the two distances travelled. Explain why this type of evidence is excellent support for the theory of relativity.

2. Relevant equations

tm = ts/ sqrt(1-v^2/c^2)

3. The attempt at a solution

a) (0.99)(3x10^8) = v
v = 2.97x10^8

v=dt
d = (2.97x10^8)(2.2x19^-6)
d = 653.4 m

b) tm = ts/ (1-v^2/c^2)
tm = 2.2x10^-6/0.141
tm = 0.000015602 s

c) d = vt
= (2.97x19^-6)(1.56x10^-6)
= 463.32 m

d) ?

2. Jan 25, 2015

### BvU

What are you calculating in (b) ? The expression is not your relevant formula and the calculation is way off !
Fix that and then c and d will be a lot more doable.

3. Jan 26, 2015

### DEvens

Ok, couple typos there. You forgot the square-root sign. And it might be helpful if you converted your tm into scientific notation.

The (2.97x19^-6) looks like you intended to write (2.97x10^8) but your fingers got away from you.
Check the (1.56x10^-6) .