31. In the system shown in Figure P5.31, a horizontal force F acts on the 8.00-kg object. The horizontal surface is fric- tionless. Consider the acceleration of the sliding object as a function of F. (a) For what values of F does the 2.00-kg object accelerate upward? (b) For what values of F, is the tension in the cord zero? (c) Plot the acceleration of the 8.00-kg object versus F. Include values of F, from -100 N to +100 N. 2.00 kg 8.001 kg Fx