# Work done in circular motion

1. Oct 20, 2009

### songoku

1. The problem statement, all variables and given/known data
A body of mass m moves at constant angular speed $$\omega$$ in a horizontal circle of radius r. What is the work done on the body in one revolution?

a. zero

b. $$2\pi mr^2\omega ^2$$

c. $$\pi mr^3\omega ^3$$

d. $$mr^2 \omega ^2$$

e. $$mr^2 \omega ^2 /2$$

2. Relevant equations
W=F.s

3. The attempt at a solution
Because the displacement is zero, then the work done is zero?

Thanks

2. Oct 20, 2009

### Staff: Mentor

What direction is the force on the body? What direction does the body move?

Or: Consider the change in the body's kinetic energy.

3. Oct 20, 2009

### Fightfish

Yup. Another way to see it is that the centripetal force does not change the energy of the body.

4. Oct 20, 2009

### theJorge551

Yes. You must look at the directions of the centripetal force, and the direction of velocity, and you find your answer.

5. Oct 20, 2009

### songoku

Hi all

The direction of centripetal force is towards the center of circle and direction of motion is tangential to the circle.
So, it means that the work done is always zero because the force is perpendicular to the direction of motion?

Thanks

6. Oct 20, 2009

Right!