One kind of elevator has the elevator car hanging from a...

One kind of elevator has the elevator car hanging from a cable, which then passes over a pulley and connects to a counterweight, as shown in (Figure 1). The mass of a fully-loaded elevator (that is, the elevator and all its passengers) is 1900 kg , the mass of the counterweight is 1650 kg , and the pulley has a radius of 0.6 m and a mass of 350 kg . A motor drives the motion of the elevator by exerting a torque on the pulley. Assume that friction is negligibe. counter weight elevator

Transcript

00:01 All right, so it doesn't appear that there's a problem here.

00:06 It doesn't ask to find anything in this screenshot that was provided.

00:13 However, i did do a search for similar problems and found that it was asking for torque given the acceleration.

00:22 And so i'm going to solve this generically for the torque provided by the motor when the elevator is going up and when the elevator is going.

00:30 Is coming down and then hopefully i'll explain it clearly enough that you can take it from there.

00:37 So in this problem, we have three elements.

00:43 So we have the elevator, we have the counterweight, and we have the pulley.

00:47 And so looking at the upcase first, when we're lifting the elevator up, the net force on the elevator is going to be its mass times its acceleration, and that's going to equal the tension force minus its weight force.

01:02 Again, we're lifting the elevator up.

01:06 For the counterweight, its mass times its acceleration will equal its weight force minus the tension force in this string right here.

01:17 And then finally, we have a net torque on the pulley provided by the motor, and that net torque will be equal to the torque due to tension two minus the torque due to tension 1, which can be found by taking the radius times the tensions in each of those strands.

01:45 And so this is going to be the torque on this pulley.

01:50 So we can solve each of these in terms of tensions...

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