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 ?

 

[rwisz]

I would say that the work done by a radial force is determined by the displacement of the object in the direction of the force. In this case, the displacement is perpendicular to the direction of the force, so the work done is zero. This is because the dot product of the force and displacement vectors is zero. Therefore, the correct answer is A) zero.