A simple pendulum is made by attaching a small cup of sand with a hole in the bottom of a 1.2 m long string. The pendulum is mounted on the back of a small motorized car. As the car drives forward, the pendulum swings from side to side and leaves a trail of sand (15 cm from bottom of wave to bottom of wave) How fast was car moving?

Question

A simple pendulum is made by attaching a small cup of sand with a hole in the bottom of a 1.2 m long string.  The pendulum is mounted on the back  of a small motorized car.  As the car drives forward, the pendulum swings from side to side and leaves a trail of sand (15 cm from bottom of wave to bottom of wave) How fast was car moving?