Angular Velocity and Acceleration for Elevator Mechanism

[YamiBustamante]

Homework Statement

In a charming 19th-century hotel, an old-style elevator is connected to a counterweight by a cable that passes over a rotating disk 3.50m in diameter (the figure (Figure 1) ). The elevator is raised and lowered by turning the disk, and the cable does not slip on the rim of the disk but turns with it.

a) At how many rpm must the disk turn to raise the elevator at 15.0cm/s ?

b) To start the elevator moving, it must be accelerated at 1/8g. What must be the angular acceleration of the disk, in rad/s^2?

c) Through what angle (in radians ) has the disk turned when it has raised the elevator 3.10m between floors?

d) Through what angle (in degrees ) has the disk turned when it has raised the elevator 3.10m between floors?

Homework Equations

E = (1/2)Iw^(2)
I = (1/2)mR^(2)
w = v/R

The Attempt at a Solution

I tried using w = v/R but it didn't work! I even converted it to rpm but got the wrong answer!

 

[AlephNumbers]

I tried using w = v/R but it didn't work! I even converted it to rpm but got the wrong answer!

a) At how many rpm must the disk turn to raise the elevator at 15.0cm/s ?

Post your work, please. Keep in mind that rpm is revolutions per minute. The velocity you are given is in cm/s.

 

[YamiBustamante]

Post your work, please. Keep in mind that rpm is revolutions per minute. The velocity you are given is in cm/s.

I made a calculation mistake! The answer is 0.82 rpm

 

[haruspex]

I made a calculation mistake! The answer is 0.82 rpm

So is this thread done, or do you still have questions?

 

[YamiBustamante]

So is this thread done, or do you still have questions?

It's done :D