app.rb

require_relative('./car')

bmw = BMW.new("M4")

begin
	bmw.accelerate
	bmw.accelerate
rescue => e
	puts e
end

car.rb

class Car
	class TooFastException < StandardError
	end

	def initialize(model, top_speed)
		@model = model
		@top_speed = top_speed
		@current_speed = 0
	end

	def accelerate(how_fast)
		raise TooFastException, "Car is too fast" unless (@current_speed + how_fast) > @top_speed
		@current_speed += how_fast
	end
end

class BMW < Car
	def initialize(model)
		super(model, 255)
	end

	def accelerate
		super(120)
	end
end