00:01
So in this question, we have an elastic collision between two tennis balls.
00:05
One is, let's call it, a 0 .060 kilogram that is initially moving with the speed of 5 .50 meters per second.
00:16
And it has head -down collision with another ball that is 0 .090 kilogram that is moving, oh, it's moving in the same direction.
00:29
Round arrow, sorry.
00:32
So it's moving in the same direction with a speed of 3 meters per second.
00:38
0 .090 kilogram.
00:41
So since it's moving slow, 6b is moving slower than a will catch up and collide with it.
00:47
So they will have a perfectly elastic collision and we want to know the speed in direction of each ball after the collision.
00:54
So again, this is, this whole thing is about section 4 and section 5.
00:59
And there are two formulas we need to use.
01:01
One is formula 7.
01:04
This is a derivation from the conservation of energy.
01:07
This is true for all elastic collisions.
01:10
This is that the relative velocity between two objects will be equal and opposite before and after the collision.
01:19
So this is a formula that will apply for all elastic collisions.
01:24
And the second is just the conservation of momentum.
01:28
So usually what we do is we will use formula 77 to express va prime or v8 prime will express one term in terms of the other.
01:43
Then we will substitute the expression into the conservation formatum, such as just the recipe for all elastic condition questions.
01:52
So we will do the same here.
01:54
So the first step, we have v .a.
01:58
Minus vb equals negative va prime, peresis, minus ve, vb prime...