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Need help in Unit Vectors

  • Thread starter snowrock
  • Start date
2
0
1. Homework Statement

The cable AB keeps the 8-kg collar A in place on the smooth bar CD. The y axis points upward. Determine the distance s from C to the collar A for which the tension in the cable is 150N.
location of:
B: (0m, 0.5m, 0.15m)
C: (0.4m, 0.3m, 0m)
D: (0.2m, 0m, 0.25m)

collar A's location is unknown. The required is the distance between C and collar A. The answer is 0.305m, but I need the solution for it.
For an easier look, http://img86.imageshack.us/img86/4710/392ij8.jpg" [Broken]

Someone answered this in yahoo answers. Can someone verify it?
http://answers.yahoo.com/question/index;_ylt=AgV3Ti6P9WnWMOA1BU8rsIDzy6IX?qid=20061225063557AANnWr1"

2. Homework Equations

e dc= dc/|dc|
W=mg
edc=eac
s=distance between A and C

3. The Attempt at a Solution

DC=0.2i+0.3j-0.25k
e dc=0.4558i-0.6838j+0.5698k
I'm not sure about this part...
eab= -Axi+(0.5-Ay)j+(0.15-Az)k
sqrt(Ax^2+Ay^2+Az^2-Ay-0.3Az+0.2725)
eac= (0.4-Ax)i+(0.3-Ay)j-Azk
sqrt(Ax^2+Ay^2+Az^2-0.8Ax-0.6Ay+0.25)

sedci=-150eabi
sedcj=-150eabj
sedck=-150eabk

eabi=-Axi/|AB|
eabj=(0.5-Ay)j/|AB|
eabk=(0.15-Az)k/|AB|

I equated the "s" in the previous part and got...
Ay=0.5-1.5Ax
Az=1.25Ax+0.15
After that, my solutions just go in circles. I couldn't get what Ax is.
Also, Is my use of Ax, Ay, Az correct? I'm doubting about it.
 
Last edited by a moderator:

Astronuc

Staff Emeritus
Science Advisor
18,547
1,682
The weight of the collar acts downward, but the movement of the collar is contrained by the rod between C&D, so one must find the force component along C&D, which acts toward D.

The tension in AB has a component which acts upward toward C.

For a static situation, the corresponding x, y, and z components of the forces must = 0.
 

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