16. A force of F = 20x - > N stretches a nonlinear spring by x meters. What work is required to stretch the spring from x = 0 to x = 2 m? 17. Find the work done when you push a box along the floor 2 m, when you apply a constant force of F = 100 N. 18. What is the work done moving a particle from x = 0 to x = 1 m if the force acting on it is F = 3x N? 19. A cylinder of depth / and cross-sectional area A stands full of water at density p. Compute the work to pump all the water to the top. 20. For the cylinder in the preceding exercise (problem 18), compute the work to pump all the water to the top if the cylinder is only half full