Which angular equation requires radian measure

[gcombina]

Homework Statement

Which equation is valid only when the angular measure is expressed in radians?
a) α = Δθ / Δt

b) ω= Δω / Δt

c) ω^2 = ωo^2 + 2αθ

d) ω = Vt/r (here T is a subscript)

e) θ = 1/2αt^2 + ωαt

Answer is D but why??

Homework Equations

I know angles can be measured in either degrees or radians

The Attempt at a Solution

angular velocity = ? divided by radius

I guess I don't understand what Vt is

 

[Vagn]

Homework Statement

Which equation is valid only when the angular measure is expressed in radians?
a) α = Δθ / Δt

b) ω= Δω / Δt

c) ω^2 = ωo^2 + 2αθ

d) ω = Vt/r (here T is a subscript)

e) θ = 1/2αt^2 + ωαt

Answer is D but why??

Homework Equations

I know angles can be measured in either degrees or radians

The Attempt at a Solution

angular velocity = ? divided by radius

I guess I don't understand what Vt is

How do you relate the length of an arc to the angle subtended by the arc and the radius? What should the units of each quantity be?

 

[gneill]

I guess I don't understand what Vt is

Presumably $V_t$ will be defined in the text surrounding the problem. In this context I would imagine that it represents the tangential velocity of a rotating object at distance r from the center of rotation.