One end of a horizontal spring (k = 333 N/m) is attached to a 3.12 kg box, and the other end to a fixed, vertical wall. (A picture of this situation can be found in Fig 4-10 on page 102 of your textbook.) a) Find the magnitude of the force needed to move the mass so the spring is stretched by 7.15 cm. b) Suppose the spring is stretched 7.15 cm and released. When the spring is stretched by only 2.88 cm, what is the acceleration of the mass? Tried it plugging in the given quantities into hookes equation, doesn't work out that way. How do I approach this one? Here is what I'm thinking so far: F=ma where F in this case is the same F in hookes equation, thus: -kx= ma Am I on the right track here?