00:01
All right, so the first step in this problem is figuring out how much energy is going to be, or how fast this big ball is going to be moving when it hits the cannonball.
00:11
We can use conservation of energy to figure that out.
00:13
We release this from rest.
00:15
Its initial potential energy is mgh, or this is the h2, or how high out the ground it's been pulled.
00:24
And its final energy, it'll have no more potential energy when it hits, and it'll have a kinetic energy just before an impact.
00:30
And so solving this for v, call that v1.
00:34
This is how fast this 80 kilogram ball will be going when it hits the cannonball.
00:40
Next, we need to know how long it takes for this little, the cannonball to reach the ground, to go a distance each one.
00:49
And we can figure that out by using our kinematic equation, vertical displacement.
00:55
So we're going a distance of negative h.
00:57
The initial speed is going to be zero in the y direction.
01:04
And solving this for time, since this term goes away, we can solve for t.
01:13
We're going to get t is equal to 2h1 over g.
01:20
And now looking at the x direction here, the velocity of this ball right before it goes, we can find by conservation and momentum and energy between this collision.
01:34
So v2, the velocity here, it's going to be 2 times mv1.
01:38
Of this one, divided by the combined mass.
01:43
And you can derive this yourself by starting with the conservation of momentum between the collision and the conservation of energy between the collision, since it's an elastic collision and solve for v2 in terms of v1.
02:00
And now we can substitute this for v1, and we get an expression for v2 in terms of m, little m, and h2.
02:16
The range here is going to be v2, the speed of the cannonball right after the collision, times the time that it's in the air.
02:24
So this v2 right here times this time right here.
02:30
We plug those in.
02:32
We can simplify this expression because there is a g, a numerator, a square root g over a square root g, so those cancel out...