# Wheel on a game show force problem

1. Apr 17, 2005

### med9546

A wheel on a game show is given an initial angular speed of 1.3 rad/s. It comes to rest after rotating through 3/4 of a turn. Find the average torque exerted on the wheel given that it is a disk of radius 0.80m and mass of 6.4 kg. I worked the matching problem in the book and got the right answer. However when I plugged in my number (the ones above) from my homework it didn't come out right. What is going wrong. I used
w^2=w(initial)^2 + 2(alpha)(delta theta)
Then I found I by using I = (1/2)mr^2
I them multiplied the two answers together to get the torque since
Torque = I(alpha)

Like I said, this worked to find the answer using the books numbers but it didn't work for my homework. (The books numbers are (W final = 0 rad/s, w initial = 1.22 rad/s, radius is 0.71m. The rest is the same. The answer is 0.25) Please help

2. Apr 17, 2005

### dextercioby

$$\delta\theta=\frac{3}{4}2\pi \ \mbox{rad}=\frac{3\pi}{2} \ \mbox{rad}$$

$\alpha$ is negative and the torque will be negative is well.

Daniel.