feat: add delta x motion equation implementation

Fixes: #191

Author: nickzerjeski

maths/delta_x.rb

@@ -0,0 +1,11 @@
+# frozen_string_literal: true
+
+# Computes displacement from uniformly accelerated motion:
+# delta_x = v0 * t + 0.5 * a * t^2
+class DeltaX
+  class << self
+    def call(initial_velocity:, time:, acceleration:)
+      (initial_velocity * time) + (0.5 * acceleration * time * time)
+    end
+  end
+end

maths/delta_x_test.rb

@@ -0,0 +1,18 @@
+# frozen_string_literal: true
+
+require 'minitest/autorun'
+require_relative './delta_x'
+
+class DeltaXTest < Minitest::Test
+  def test_zero_acceleration
+    assert_in_delta 15.0, DeltaX.call(initial_velocity: 3.0, time: 5.0, acceleration: 0.0), 1E-12
+  end
+
+  def test_positive_acceleration
+    assert_in_delta 20.0, DeltaX.call(initial_velocity: 2.0, time: 4.0, acceleration: 1.5), 1E-12
+  end
+
+  def test_negative_acceleration
+    assert_in_delta 2.0, DeltaX.call(initial_velocity: 5.0, time: 2.0, acceleration: -4.0), 1E-12
+  end
+end