Final answer:
The magnitude of the acceleration is 400 m/s^2.
Step-by-step explanation:
The magnitude of acceleration in circular motion can be determined using the formula:
ac = v^2 / r
where ac is the centripetal acceleration, v is the velocity of the particle, and r is the radius of the circle.
In this case, the velocity of the particle is 20 m/s and the radius of the circle is 10 m. Substituting these values into the formula, we get:
ac = (20 m/s)^2 / 10 m = 400 m/s^2
Therefore, the magnitude of acceleration is 400 m/s^2.