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whatname
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Homework Statement
this is from an example problem in the hibbler dynamics book 13th edition in the section of work so i don't really have a question on how to do it. the question is why is the problem solved the way it is solved.
the system has one pulley.one rope.and two masses at each end of the rope the work done by gravity is positive for both masses...why?. since one mass is going up and the other mass down. shouldn't work by gravity be negative for the mass going up?
i assign positive going down.
Homework Equations
work done on an object = the change in the objects KE
The Attempt at a Solution
i solved with kinematic equations and found the answers match. so I know its correct to assume that both masses go down with energy equations, but if I try to solve with one mass going up (and so work by gravity is negative on that one)and the other down (so work by gravity is positive on this one) using energy equations I get a different/wrong answer. so why must both masses be assumed to move down? is it because of the rope? How? also, tension does zero work. Why? is it because its a reaction force? can reaction forces do work?