In part (a) I considered the components of my system to be the two blocks and the Earth, but in part (b) I considered only mass 2 and the Earth. I treated it as an isolated system, however. I wrote that change in kinetic energy = - (change in potential energy). So, why did this equation work...
I would think the weight of mass 1 is pulling the other block up? The table also exerts a force on mass 1. Is that the force that makes it lose velocity and reach v = 0? Will the isolated system model stop being valid once mass 1 has touched the table?
I have some conceptual questions about this task. In order to get the correct result (I checked the textbook answer) in part (a) I had to assume that the speed for each block is the same at all instants. And that if one block moves down x meters, the other one will move up that same amount of...
I see. I realize I had incorrectly assumed D and U had the same direction, but they have opposite ones. I also had incorrectly written -29.4 in the torque equation when it should had been +29.4. I re-calculated it and now I get the correct result. Thanks.
The way I thought about it is: if it's a reaction force, it means it's reacting to an original force ("action") exerted by body one. The "action" force is the one that is applied by body one to body two. Then body two generates a reaction force that acts on body one. This is what I mean with...
The question doesn't specify whether we're talking about translation or rotational equilibrium, so I suppose it's both: In order for the body to have translational equilibrium:
60 N + F2 = 0
F2 = -60N
However, in order to have rotational equilibrium:
60 N * 3m + F2 *8 m = 0
60 N * 3m - 60 N...