# Which radius (r or R) should you use? Why?

1. Nov 12, 2008

### shimizua

1. The problem statement, all variables and given/known data
A rolling wheel of radius r has translational velocity v as well as angular velocity w. Here you will relate translational velocity to angular velocity. Since the circumference of a circle of radius r is 2p r, every time the center of mass moves a distance 2p r, the object rotates a full circle (2p radians). If this happens in a time T then
v = Dx/Dt = 2p r / T (1)
and w = Dq/Dt = 2p/T (2)
Combine these equations to find an expression for w in terms of v.

2.When applying equation 1 (in question 1) to our system, which radius (r or R) should you use? Why?
2. Relevant equations
so i figured out the first question, i was just putting it up so you knew what was going on. But as far as equations i dont think there would be any for this question

3. The attempt at a solution
I think it should be r since in the equation and statment they only refer to r and not R

2. Nov 12, 2008

### jgens

Just divide the two equations and solve the resulting equation for w.