A spring on a horizontal surface can be stretched and held 0
     A spring on a horizontal surface c.an be stretched and held 0.8 m from its equilibrium position with a force of 64 N.  How much work is done in stretching the spring 3.5 m from its equilibrium position?  How much work is done in compressing the spring 1.5 m from its equilibrium position?  The amount of work done is  J. (Simplify your answer.)   
  
  Solution
k = 80 0.5kx^2 = W a) 490 J b) 90J
