The period of a pendulum is the time it takes the pendulum to make one full swing back and forth. The period T, in 54 L seconds, is given by the formula T = 2π where L is the length, in feet, of the pendulum. Suppose a pendulum used 32 to show the rotation of the earth has a period of approximately 19.6 seconds. What is its length? Use 3.14 for . 11 The length of a pendulum that has a period of 19.6 seconds is feet.