00:01
So let's say we have a pulley suspended from the ceiling and there's a four kilogram block on one side, a two kilogram block on the other side.
00:10
And i tell that the pulley experiences a frictional torque of 0 .45 newton meters.
00:17
It has a radius of 7 centimeters.
00:21
And let's see what else.
00:22
It has a mass of 2 kilograms.
00:24
And so we want to know if this taller block is initially 1 meter off the ground.
00:28
How long will it take it to hit the ground when these.
00:30
Are released so it's called block one this call us block two then the tension in this side is t1 the tension in this sign is t2 and so the torque on the pulley is going to be t1 minus t2 minus or sorry those are our tensions times the radius minus the frictional torque we'll just call this tau and this should equal the the moment of inertia times the angular acceleration and our moment of inertia for a rod like this is just going to be one half m r squared and we can write the angular acceleration as a over r so really we'll have one half m r a or sorry capital m so and then if we look at the tensions what are the tension is going to be uh t1 is going to be like m1 g minus or sorry m1a minus g and then t2 is going to be m2 g minus a um because we can see the acceleration is going to be in the, or sorry, this should be g minus a, and this one should be a minus g.
01:40
Because we can see the acceleration of like block two should be in the same direction as the tension, which we have there...