- #1

inner08

- 49

- 0

## Homework Statement

A wheel is turning initially at 1200 turns/min and stops in 4 min because of friction. If we add a supplementary torque of 300 N*m, the wheel stops in 1 min.

a) What is the moment of inertia of the wheel?

b) What is the torque of friction?

## Homework Equations

Torque = alpha * I

time = w/alpha

f = ucF

Torque = -fR

## The Attempt at a Solution

I figured i'd start by converting the 1200 turns/min into rad/sec

(1200 *2pi)/60 = 126 rad/sec (this gives me angular speed - w)

Then I figured i'd find the angular acceleration using the angular speed that I just found with the time it takes to stop (in this case its 4min or 240seconds).

alpha = 126/240

= 0.525

Now at first I thought I could just substitute these in the equation Torque = alpha * I but it doesn't work out.

I then realized that they are saying that there is a SUPPLEMENTARY torque and it then stops in 1min. I thought it would then be something like "initial torque + 300 = something...". Does that make any sense?

Any help to clear this up would be appreciated!