# Homework Help: Speed of discus being thrown

1. Oct 14, 2008

### mastiffcacher

1. The problem statement, all variables and given/known data
To throw the discus, the thrower holds the discus with a fully outstretched arm and makes one revolution as rapidly as possible to give maximum speed to the discus at release. The diameter of the circle in which the discus moves is about 1.8 . If the thrower takes 1.1 to complete one revolution, starting from rest, what will be the speed of the discus at release?

2. Relevant equations
I am not sure where to begin. I know that angular velocity=change of theta/change in time.

3. The attempt at a solution
I keep on getting 5.14 m/s. The answer given by the computer is 10 m/s. The only way that I can get 10 m/s is if you use r=1.8 m. I thought the radius would be half the diameter of the circle. What am I missing and what did I do wrong?

2. Oct 14, 2008

### mgb_phys

Remember the circumference of a circle is 2 pi r

3. Oct 14, 2008

### mastiffcacher

I see that but it still leads to (2*pi*.9)/1.1 s=5.14 m/s. If you use 1.8 as the radius then it works out to 10.28 m/s. I have already missed this question in my homework so I am just trying to figure how they got what they got.

4. Oct 14, 2008

### mgb_phys

Yes you're right - looks like they made a mistake in the question.