question.rb1 question :a_whirled_stone do2   kind :numerical3   describes "A stone on a string %{length} long is whirled round a horizontal circle at a steady speed, %{turns} times in %{time}. %{acceleration}, in m/s2?"4   given length: "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 6   take length: circle.radius, turns: stone.revolutions, time: stone.goes(:spinning, on: circle).time_taken7   deduce_from "14 times in 25 s", stone.revolutions => 14.0, stone.goes(:spinning, on: circle).time_taken => "25 s"8 9   acceleration = stone.centripetal_acceleration10   answer acceleration:, in: "m/s2", figures: 311   conclusion "The stone moves at a steady speed but its direction changes constantly, so it has a centripetal acceleration toward the centre."12 end