An 0.80-kg block is held in place against the spring by a 67-n horizontal external force (see the figure. the external force is removed, and the block is projected with a velocityv1 = 1.2 m/s upon separation from the spring. the block descends a ramp and has a velocity v2 = 1.9 m/s at the bottom. the track is frictionless between points a andb. the block enters a rough section atb, extending toe. the coefficient of kinetic friction over this section is 0.39. the velocity of the block isv3 = 1.4 m/s atc. the block moves on tod, where it stops. the spring constant of the spring is closest to