# Motion in a circle

1. Jul 12, 2007

### Edwardo_Elric

1. The problem statement, all variables and given/known data
A model of a helicopter rotor has four blades, each 3.20m in length from the central shaft to the blade tip. The model is rotated in a wind tunnel at 600rev/min. a.) What is the linear speed of the blade in m/s?
b.) What is the radial acceleration of the blade expressed as a multiple of the acceleration due to gravity g?

2. Relevant equations
$$a_{rad} = \frac{V^2}{R}$$
$$a_{rad} = \frac{4{\pi}^2R}{T^2}$$

3. The attempt at a solution
a.) convert: 600rev / min ( 1 min / 60secs) = 10 rev / s
Multiplied 3.20m by 10 rev / s = 32.0m/s?

b.) $$a_{rad} = \frac{V^2}{R}$$
a_{rad} = (32.0m/s)^2 / (3.20m) = 320m/s^2

i dont understand the radial acceleration of blade expressed as a multiple of g....

2. Jul 12, 2007

### Staff: Mentor

Careful. To convert between linear and angular speed, use $v = \omega r$, where $\omega$ is in radians/sec, not rev/s.

Alternatively, realize that 1 revolution covers 1 circumference, which equals $2 \pi r$.

Redo this with the correct speed.

Since g = 9.8 m/s^2, just divide your answer by that value to get an answer as a multiple of g.