Francisco P. answered 09/17/14
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Rigorous Physics Tutoring
The arc length is related to the radius and angle (in radians) by the formula, s = rθ.
θ = s/r = 5m/2m = 2.5 rads
The angular velocity (speed) is then the angle advanced divide by the time it took: ω = θ/t = 2.5 rads/20 s = 0.125 rads/s