question.rb1 question :a_whirled_stone do2   kind :numerical3   describes "A stone on a string %{radius} long is whirled round a horizontal circle at a steady speed, %{turns} times in %{time}. %{acceleration}, in m/s²?"4   given radius: "80 cm"5   given turns: 14.06   given time: "25 s"7   asks acceleration: "What is its acceleration"8 end

solution.rb1 solve :a_whirled_stone, using: UniformCircularMotion do2   objects :stone3   paths :circle4   stone.goes(:round, on: circle)5   take radius: circle.radius, turns: stone.revolutions, time: stone.goes.time_taken6   deduce_from "14 times in 25 s", stone.revolutions / stone.goes.time_taken => "14.0 / 25.0"7   acceleration = stone.centripetal_acceleration8   answer acceleration:, in: "m/s2", figures: 39   conclusion "Its speed never changes, but its direction always does, and that turning is an acceleration pointed at the centre of the circle."10 end