# Homework Help: Problem with average velocity in a circle

1. Sep 28, 2004

### DuffBeer

A particle P travels with constant speed in a circle of radius 7.4 m and completes one revolution in 22.0 s (see Figure). The particle passes through O at t = 0 s. What is the magnitude of the average velocity during the interval from t = 4.4 s and t = 18.7 s.

I used T=2(pi)r / v

22 = 2*pi*7.4/v
v = 2.11 m/s

But the answer was rejected... The velocity in a circle is supposed to be constant, why won't my answer work?

2. Sep 28, 2004

### Staff: Mentor

The speed is constant, not the velocity.

3. Sep 28, 2004

### DuffBeer

Oh man... Does that mean my answer is just negative since it's moving counterclockwise?

4. Sep 28, 2004

### Staff: Mentor

find the displacement

No. I suspect they want you to find the net displacement of the particle from t = 4.4 s to t = 18.7 s. Find out where it is on the circle at those two points, and then figure the displacement. The "average velocity" will be the net displacement divided by the time.