Three students are debating: student a: the pressure at level c must now be greater than the atmospheric pressure because liquid there is being pushed up against the stopper. student b: i think the pressure at level b must be the same as at level a, because they are at the same level. both are at atmospheric pressure. so the pressure at level c must be lower than atmospheric, because pressure decreases as you ascend. student c: but the liquid is denser than air, so the pressure at c cannot be less than atmospheric pressure. with which student(s) should you agree?

As you are trying to move a heavy box of mass m, you realize that it is too heavy for you to lift by yourself. there is no one around to , so you attach an ideal pulley to the box and a massless rope to the ceiling, which you wrap around the pulley. you pull up on the rope to lift the box. use g for the magnitude of the acceleration due to gravity and neglect friction forces. once you have pulled hard enough to start the box moving upward, what is the magnitude f of the upward force you must apply to the rope to start raising the box with constant velocity? express the magnitude of the force in terms of m, the mass of the box.