I'm trying to understand a problem in my physics book. The problem is this:A person is pulling on a rope, that is connected to a pulley on the ceiling. The rope then goes to a box with a pulley on it, and then up to the ceiling where the rope is connected (to the ceiling).The rope and pulleys are massless and frictionless.The book lists three forces (tension forces) going up and one weight force pulling down.My question is, why isn't there another force pulling against the tension of the rope from the guy pulling the rope?
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well, the person is going to have to pull on the rope, and that will be another force that is not pictured in the book. if you think about it, when a rope is under tension, each end is getting pulled, like a tug of war, otherwise it just moves toward the other force. When the forces are balanced, the rope is in tension and does not move. The forces pictured in the book are tension provided by the weight. The person will have to add a tension force downward to compensate.
The force felt by the person pulling is the same as the force in the rope between the two pulleys. It doesn't matter if the person is pulling straight up (without the pulley) or straight down(with the pulley) it's the same. Therefore the weight/force is divided equally between the two ropes.
