- #1
P3X-018
- 144
- 0
I have this problem, which I think I can solve in 2 ways, but only 1 of them seems to be correct, but I don't understand why the other isn't correct. The problem is as follows:
"A bar with the rest length L_0 moves in its length direction with the velocity v through a lab. A particle moves along the same line but in opposite direction with the same speed v [velocity -v]. How long will it take the particle to pass the bar, [time] mearsured from the lab."
The easy way to do this, is by saying that if L is the length of the bar seen from the lab, then the time the particle will take to pass the bar will be
[tex] T = \frac{L}{2v} = \frac{L_0}{2v\gamma} [/tex]
(this is also the result given in the solutions manual)
But if we look at the situation from the bars reference frame, then the particle will be moving with a velocity
[tex] v' = \frac{2v}{1+v^2/c^2} [/tex]
So the time the particle will take to pass the bar seen from the bars intertial frame will be
[tex] T' = \frac{L_0}{v'} = \frac{L_0(1+v^2/c^2)}{2v} [/tex]
This time T' seen from the lab most be
[tex] T = \gamma T' = \gamma(1+v^2/c^2)\frac{L_0}{2v} [/tex]
But this last result ain't equal to the first one. Why is that so? Where did I make a mistake in my last calculations?
"A bar with the rest length L_0 moves in its length direction with the velocity v through a lab. A particle moves along the same line but in opposite direction with the same speed v [velocity -v]. How long will it take the particle to pass the bar, [time] mearsured from the lab."
The easy way to do this, is by saying that if L is the length of the bar seen from the lab, then the time the particle will take to pass the bar will be
[tex] T = \frac{L}{2v} = \frac{L_0}{2v\gamma} [/tex]
(this is also the result given in the solutions manual)
But if we look at the situation from the bars reference frame, then the particle will be moving with a velocity
[tex] v' = \frac{2v}{1+v^2/c^2} [/tex]
So the time the particle will take to pass the bar seen from the bars intertial frame will be
[tex] T' = \frac{L_0}{v'} = \frac{L_0(1+v^2/c^2)}{2v} [/tex]
This time T' seen from the lab most be
[tex] T = \gamma T' = \gamma(1+v^2/c^2)\frac{L_0}{2v} [/tex]
But this last result ain't equal to the first one. Why is that so? Where did I make a mistake in my last calculations?