# Homework Help: Another Equlibrium topic

1. Dec 8, 2006

### PremedBeauty

A stationary arrangement of two crayon boxes and three cords. Box A has a mass of 11.0kg and is on a ramp at angle θ=30.0 degrees; box B has a mass of 7.00 kg and hangs on a cord. The cord connected to Box A is parallel to the ramp which is frictionless (a) What is the tension in the upper cord, and (b) what angle does that cord make with the horizontal?

Let TA = tension force in the cord attached to block A.
TB = tension force in the cord attached to block B.
TC = tension force in the cord attached to ceiling.
φ = angle of cord attached to ceiling with the horizontal
θ = angle of ramp = 30 degrees

1.Ta-magsin
2.Tb-mbgsin=0
3.Tcsin=magsin+mbg
4.Tccos=magsin
5=T^2c(cos^2+sin^2)

that's what I know so far (on what equations to use for each step)

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Last edited: Dec 8, 2006
2. Dec 8, 2006

### OlderDan

I think you need to modify your diagram. The cord connected to A should be parallel to the ramp. The cord connected to B is vertical, but far enough to the right so that B is not in contact with the ramp (you're OK with this one) and the cord supporting the whole thing is NOT vertical. It makes whatever angle is needed to produce equilibrium. You need to have angles after your cos and sin in your equations so you know which angle you are talking about.