00:01
We have an elevator descending down a shaft at a constant speed, and it's being supported by a single cable.
00:07
I've done that as this yellow line, which of the following is true.
00:12
These are all about work.
00:18
Now the guiding principle here is that the velocity is constant.
00:27
That's really important.
00:28
So if you know that the velocity is constant, this tells you, basically tells you the answer.
00:33
So we can use the work energy theorem, which tells us the network on an object is equal to its change in kinetic energy.
00:47
Now, kinetic energy depends on mass and velocity.
00:50
And if we assume that the mass is constant, which it is, then the change in kinetic energy just depends on the velocity squared.
01:02
Well, if the velocity is constant, then what's the change in kinetic energy? zero, right? so if the change in kinetic energy is zero, that tells you that the network is zero, which looks to be option e here...