What is the work done by a radial force in this situation?

[dinhjeffrey]

Homework Statement

http://img26.imageshack.us/i/1113001.jpg/

#11

Homework Equations

C = 2πr
w=fd

The Attempt at a Solution

it travels from point 1 to 2 so its half a circle so the distance is πR.
πRF = w
so i would guess its D.
but the answer is A) zero. i do not know why it is zero though.

 

[rock.freak667]

Hint: the force is radial, but which direction is the particle at ? (radial, tangential or other)

 

[dinhjeffrey]

Hint: the force is radial, but which direction is the particle at ? (radial, tangential or other)

tangential, oh so the work done would be by the tangential force, not the radial force?

 

[rock.freak667]

tangential, oh so the work done would be by the tangential force, not the radial force?

No, there is only the radial force, but the instantaneous direction of the particle is given by the direction of the tangent.

So if the force is perpendicular to the direction, what is the work ?