00:01
Oh, here we have to solve the following problem.
00:03
Disc has a mass of 2 .6 kilograms.
00:08
Let's call it mp, which stands for the pulley.
00:14
And the stone has a mass of 1 .9 kilograms.
00:23
In question a, we have to find how far the stone must fall, so the kinetic energy of the pulley is four and a half joules.
00:38
Let's calculate it.
00:41
So it means that this mgh, decreasing potential energy of the stone, must be equal to the kinetic energy of the stone plus rotational energy of the pulley.
00:57
Now let's rewrite it.
01:08
And here let's basically look at the kinetic energy of the pulley.
01:14
That's i omega squared over 2, which is mass of the pulley, its squared radius over 2, times one half times v squared over r squared.
01:36
So then v squared is for kinetic energy of the pulley over mass of the pulley.
01:44
Now let's write down the formula for the changing potential energy of the stone.
02:00
And let's simplify this.
02:15
Now let's calculate the height h...