# Homework Help: Forces and Tension

1. Feb 4, 2009

### vivekfan

1. The problem statement, all variables and given/known data

1. In a tug of war, two men pull on a rope with 100 lb forces in opposite directions. What is the tension in the rope?

2. The Moon travels around the earth. What are the forces acting on it?

Is it the gravity of the earth and sun, gravity of earth and sun + a forward force, or Gravity of earth and sun + outward force and forward force

2. Relevant equations

These questions are conceptual, but probably deal with F=ma

3. The attempt at a solution

For question 1, I'm not sure if the tensions are additive, meaning that it is 0 because they are in opposite directions or 200. I don't know whether I should add them or would it just be 100. I don't know how to approach it.

For question two, I think that there is only the gravity of the earth and the sun because I can't think of any other force that would be acting. Please explain reasoning. Thanks!

2. Feb 4, 2009

### LowlyPion

For 1) the man pulling with 100 against another man pulling at 100 is little different that a man pulling with 100 and the rope attached to a post isn't it?

If they added then wouldn't there be acceleration somewhere if there was nothing thereto offset it?

For 2) There of course is gravity from sun and earth (and anything else in the universe). And what are these forces doing to the moon? Keeping it in orbit about the earth. If there was a forward force then it would be gaining speed. If it did that, what would happen to the obit?