00:01
All right, so we have a ball that has a mass, we'll call this ball 1, a 0 .32 kilograms.
00:09
And it's initially moving with a speed of 5 .4 meters per second.
00:16
And it strikes another ball that is stationary.
00:18
So we'll say v2 is zero.
00:20
And it has an unspecified mass.
00:22
But we're told that after the collision, ball 1 rebounds backwards with a velocity we call it's v1 prime of 3 .9.
00:31
Meters per second.
00:32
So really we'll write this as negative just to make sure we get the direction in there.
00:37
So it's moving backwards.
00:38
And so we want to know what is the mass of ball two and then what is also its velocity after the collision.
00:47
And we're told this is an elastic collision.
00:49
So that'll help us solve this.
00:51
So first off, let's write out the initial momentum of the system, which we know for momentum conservation has to be constant throughout this problem.
00:58
So it's just going to be the mass of ball one times the velocity of ball one.
01:03
And so that should give us something like 1 .728 kilograms times a meter per second.
01:11
And the final momentum of the system is going to be the mass of ball two times its velocity plus or the velocity after the collision times the mass of ball one times its velocity after the collision.
01:24
And this has to be equal to 1 .728 kilograms times a meter per second.
01:31
So if we plug in the numbers that we do have, we'll have m2v2 prime minus 0 .32 kilograms times 3 .9 meters per second.
01:47
The minus is because it's moving in the opposite direction as v2, presumably...