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View Full Version : What is the net force acting on the ring?

Max CR
Nov10-08, 07:55 PM
1. The problem statement, all variables and given/known data

http://i289.photobucket.com/albums/ll229/Cleaver97/th_001.jpg (http://s289.photobucket.com/albums/ll229/Cleaver97/?action=view&current=001.jpg)



2. Relevant equations



3. The attempt at a solution

I have absolutley no idea how to do this problem. Can anyone start me off?
marlon
Nov10-08, 07:58 PM
A Force is a vector. In this case the force can be written in terms of an x and y-component.

Write down the 3 forces in terms of x and y-components.
Once you have done that, you can calculate the net force by adding up all components in each direction.

Final step will be to calculate the magnitude of that vector

marlon
Max CR
Nov11-08, 07:43 AM
I did ...

Sin (30) = op/200
Sin (30) x 200 = op = 100
F1 = 100
F2 = Sin(60) = op/200 x 200
Sin (60) x 200 = op
173.21 = op
F2 = 173
F3 = 224

Total forces added up is 497.

What did I do wrong?? Physics test in a few hours
marlon
Nov11-08, 07:49 AM
I did ...

Sin (30) = op/200
Sin (30) x 200 = op = 100
F1 = 100
F2 = Sin(60) = op/200 x 200
Sin (60) x 200 = op
173.21 = op
F2 = 173
F3 = 224

Total forces added up is 497.

What did I do wrong?? Physics test in a few hours
I don't understand what you are doing here. What's this op ?

Force 1 : -200 e_x
Force 2 : 100 e_x
Force 3 : 200(cos30 e_x + sin30 e_y)

e_x : components in the x-direction
e_y : components in the y-direction

Do you understand the 3 above equations ?
How can you calculate the resulting net force of the 3 forces?

marlon
Max CR
Nov11-08, 08:00 AM
Force 1 : -200 e_x
Force 2 : 100 e_x
Force 3 : 100 e_y

In total it is -100 e_x, 100y, but this is not right .
Doc Al
Nov11-08, 08:06 AM
Force 1 : -200 e_x
Force 2 : 100 e_x
OK. Forces 1 and 2 are totally in the x direction, so they have no y components.
Force 3 : 100 e_y
OK, that's the y-component of Force 3. What's the x-component?
marlon
Nov11-08, 08:07 AM
Force 1 : -200 e_x
Force 2 : 100 e_x
Force 3 : 100 e_y

In total it is -100 e_x, 100y, but this is not right .

you are missing one component in force3. The 3rd force has TWO components !

marlon
Max CR
Nov11-08, 09:34 AM
F 3 is 100y and 100x
marlon
Nov11-08, 11:49 AM
F 3 is 100y and 100x

no it's not

how did you calculate this ?

you need to calculate the x and y-component of a vector

do you know how to do that ?

hint : in your answer, you'll need to calculate the sine and cosine of an angle

marlon