A body with a mass of 5.91 kg moves along the x ‑axis, influenced by a conservative force F ( x ) . → F ( x ) = A x 3 ^ x where A = − 4 N m 3 When the body is at position x i = 2.05 m, it is moving with a speed of v i = 6.01 m / s. What is the body's speed when it is at position x f = − 3.05 m?