1. The problem statement, all variables and given/known data In the figure below, a 74 kg man is on a ladder hanging from a balloon that has a total mass of 260 kg (including the basket passenger). The balloon is initially stationary relative to the ground. The man on the ladder begins to climb at 2.5 m/s relative to the ladder. (a) In what direction does the balloon move? My answer is downwards which is correct (b) At what speed does the balloon move? 2. Relevant equations vmg = vmb - vbg (where the subscripts mg refer to man relative to ground, mb man relative to balloon (ladder), and bg balloon relative to ground) vcom = [mmg - Mvbg]/M + m 3. The attempt at a solution I actually have the worked out solution to this problem but I'm finding it hard to grasp that vcom = [mmg - Mvbg]/M + m = 0 (as per my textbook solutions). This is my understanding: the balloon is stationary relative to the ground, thus the vcom of the balloon-ground system would be 0. However, the man starts to move up the ladder causing the balloon to move downward, thus changing the vcom. How can, then, the textbook solution in solving for vbg set the aforementioned equation for vcom to 0? I mean, the vbgto be calculated is not when the balloon is stationary relative to the ground, obviously, it's changing relative to the ground (moving downwards) while the man is moving up the ladder. I would appreciate help in understanding this conceptually, especially if my thinking is wrong. Thanks!