65. A cart is moving down the road, with a nail driven into one of its wheels. The diameter of the cart's wheels is 1 meter. Each time the nail hits the road, a click is heard. The clicks repeat every second. At what speed is the cart moving?
65. In 1 second, the cart travels $\pi$ meters, therefore, in 1 hour $-3.6 \pi$ km $\approx 11.3$ km per hour.