4. A spring exerts a force described by F(x) = 52.8x + 38.4x2 (N) in the opposite direction of its extension by a distance x. (a) Determine the total work needed to overcome this spring force when stretching the spring from x = 0.50 m to x = 1.00 m. (b) If one end of the spring is anchored, while the other end is attached to an object with a mass of 2.17 kg, and the spring is stretched to x = 1.00 m, then released from rest, find the speed of the object when the spring contracts back to x = 0.50 m.