Angular Acceleration Conceptual Question

[_buddha]

Homework Statement

A wheel starts from rest and spins with a constant angular acceleration. As time goes on the accerlation vector for a point on the rim:

a) decreases in magnitude and becomes more nearly tangent to the rim
b) decreases in magnitude and becomes more nearly radial
c) increases in magnitude and becomes more nearly tangent to the rim
d) increasese in magnitude and becomes more nearly radial
e) increases in magnitude but retains the same angle with the tangent to the rim

Homework Equations

At = alphaR

The Attempt at a Solution

the answer is d, but i just don't understand why. Why does an acceleration vector for a point the rim become radial ?

 

[paisiello]

Homework Statement

A wheel starts from rest and spins with a constant angular acceleration. As time goes on the accerlation vector for a point on the rim:

a) decreases in magnitude and becomes more nearly tangent to the rim
b) decreases in magnitude and becomes more nearly radial
c) increases in magnitude and becomes more nearly tangent to the rim
d) increasese in magnitude and becomes more nearly radial
e) increases in magnitude but retains the same angle with the tangent to the rim

Homework Equations

At = alphaR

The Attempt at a Solution

the answer is d, but i just don't understand why. Why does an acceleration vector for a point the rim become radial ?

Hint: The other formula is v^2/R.