# Circular motion

1. Jul 23, 2013

### Anthonyphy2013

1. The problem statement, all variables and given/known data

If the radius of theCD below is 6.0cm and the angular velocity is 5.0 rad/s , whats is its angular displacement in 2.0s ?

2. Relevant equations

Delta θ = ωt+.5∂t^2

3. The attempt at a solution
I know the angular velocity and the time but how can I find out the radial acceleration or should I use the other equation to find the angular displacement ?

2. Jul 23, 2013

### HallsofIvy

Staff Emeritus
The radial acceleration is irrelevant (and, in any case, 0 because the CD is not changing radius). If the CD is rotating at 5 radians per second, in two seconds it will have rotated through 5(2)= 10 radians. Since the CD has radius 6 cm, a point on its circumference will have moved 6(10)= 60 cm.