00:01
Okay, we have two lumps of clay, each with mass m, that are on a collision course.
00:09
Each one is moving at 0 .6 of the velocity of light.
00:14
And then they collide, and afterwards they form a single glob of mass capital m.
00:21
So after the collision, the velocity is zero.
00:26
And that agrees with conservation of momentum.
00:28
The momentum before the collision has to be the same as the momentum after.
00:33
Let's think about the energy.
00:40
So the energy before the collision for each one of them is gamma mc squared.
00:47
So gamma, 1 over square root of 1 minus 0 .6 squared, is 1 .25.
00:56
So each individual energy is 1 .25 mc squared, which is larger than what we would maybe normally expect.
01:15
In fact, if we weren't thinking relativity, the total energy would still be mc squared.
01:22
There'd be some kinetic energy in there too, however...