0:00
All right.
00:01
So in this question, we have an electron with a rest mass of just mass of the electron.
00:08
And it's been accelerated to a speed such that its total relativistic mass is now 2 .1 times its rest mass.
00:16
And the question is, what is the speed? so this comes back to this idea of relativistic mass basically just means the total energy of the particle, which can be obtained.
00:30
Using e squared equals m squared c to the fourth plus p squared c squared.
00:35
So this term, right, adds energy, or we can also say this adds what we call relativistic mass.
00:52
So quite often in things like high energy physics and particle physics, instead of using the actual rest mass of a particle, like an electron, you'll say, oh, it has this much energy because energy and mass are equivalent.
01:11
And so another thing that you'll often come into is e equals the mass relativistic of c squared, where this m relativistic, so this relativistic mass is equal to m over the square root of 1 minus b squared over c squared, which if you'll notice, that equals gamma times m.
01:40
So this gamma factor is the lorentz factor.
01:44
And so we can use this to find our v.
01:48
So we know that our, in this case, our master relativistic equals 2 .1 times the mass of the electron.
02:00
So what we can say is 2 .1 times the mass of the electron equals the mass of the electron.
02:10
Over the square root of 1 minus v squared over c squared...