A 1.6 kg mass starts from rest at point A and moves along the x-axis subject to the potential energy shown in the figure below. PE 30 J A E 25 J C 20 J 15 J D 10 J 5 J B X n 4m 6m 8m 10m (a) Determine the speed (in m/s) of the mass at points B, C, D. (For each answer, enter a number.) point B m/s point C m/s point D m/s (b) Determine the turning points for the mass. (Select all that apply. ) point A O point B O point C O point D O point E