00:01
All right, so let's say we have an atwood machine where we have two masses, and let's call us mass one and mass two.
00:09
And we're told that mass one is four kilograms, mass two is 10.
00:15
So m1 is four, m2 is ten.
00:21
And part a asks, if we were to rearrange the masses so that their heights were a little bit different, so one was a little bit lower and two was higher.
00:31
Would the potential energy be greater than less than or equal to the previous potential energy? so the potential energy we can write as like m1g times h1 plus m2g times h2.
00:46
And so if we make h1, if we make h1 lower, so we change the potential energy by writing it as like m1g h1 prime plus m2g h2b, h2 prime, where h1 prime is less than h1 and h2 prime is greater than h2, then we can figure this out because initially h2 is 0 and h1 is 20 centimeters.
01:20
So h2 has like no potential, or mass 2 has no potential energy.
01:25
And so if we were to change this arrangement, given that m2 is greater than m1, the potential energy would be greater.
01:34
It would increase as a result of this.
01:37
All right.
01:38
And so then on part b of the question, we want to know for why the masses don't spontaneously move from one configuration.
01:49
And basically it's because a change in potential energy requires a change in kinetic energy or a loss in kinetic energy.
01:58
And so if they're at a stable state, the potential energy wants to move to a lower potential.
02:07
So, like, generally speaking, the change in potential energy that is going to result is going to be negative.
02:14
But as we can see, in this case, it would require a positive change.
02:18
So it's not going to spontaneously drop to a lower potential energy.
02:22
Part c, if we move the blocks downwards, mass one downwards by an external force, what is the maximum amount of energy this force can transfer to the system, such that mass one does not hit the ground.
02:35
So basically the change in energy is really going to be the work, which is the force times the distance, which we'll call, i don't know, delta y or something like this.
02:49
And this maximum amount of energy is just going to be like m1 times g times h1.
02:55
So four kilograms, or we'll write it as 39 .2 newtons.
03:02
Times 0 .2 meters.
03:08
And so this is going to be 7 .84 joules.
03:13
That's transferred to mass 1.
03:17
But of course, that also corresponds to, let's say the change in work on mass 2 is going to be an increase in potential energy...