Question 264223
The pendulum of a clock swings through an angle of 2.5 radians as its tip travels through an arc of 50 centimeters. Find the lenght of the pendulum, in centimeters. 
r = s/angle
r = 50/2.5 = 20 cm
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Clock pendulums swing ±8º degrees or less, which is an included angle of ~0.28 radians.  Have the authors of the books ever seen a clock?