3) Figure 4 illustrates a fireman (Bill) having mass M1 standing on a scale, which is positioned on a solid horizontal surface. An ideal rope extends vertically upward from Bill's hands, up and over an ideal pulley having a fixed axis of rotation. The rope extends vertically downward from the pulley to a block having mass M2. Bill is controlling the motion of the block by pulling on the rope downward (if the block is traveling upward) or by allowing the rope to controllably slide through his hands (if the block is traveling downward).

3) Figure 4 illustrates a fireman (Bill) having mass M1 standing on a scale, which is positioned on a solid horizontal surface. An ideal rope extends vertically upward from Bill's hands, up and over an ideal pulley having a fixed axis of rotation. The rope extends vertically downward from the pulley to a block having mass M2. Bill is controlling the motion of the block by pulling on the rope downward (if the block is traveling upward) or by allowing the rope to controllably slide through his hands (if the block is traveling downward).