#1
Question is killing me... I get the feeling it's really simple but I cant think about it right.

Two dogs pull horizontally on ropes attached to a post; the angle between the ropes is 60.2 degrees.

If dog A exerts a force of 270 N and dog B exerts a force of 330 N, find the magnitude of the resultant force.

Anyone know how to solve that? I dont need an answer, just the right way to look at it.

Thanks
Originally Posted by Corwinoid
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#2
Break it into components. The total x-direction force and the total y-direction force should be zero.
#3
you need to draw a picture.
Make the forces say 27mm and 33mm long then draw a net force diagram to find the direction.

Then use trigonometry to find the size
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#4
Separate the forces into x and y directions.

i.e. 270cos(theta) = Fx1

Then add them together using i and j components (with appropriate negative values) and get the resultant vector. Then just take the magnitude sqrt(Fx^2 + Fy^2)

EDIT: Just wait until you get into a dynamics class... that's when you really will hate physics.. Ugh.. I hate dynamics.
Last edited by RockThe40oz at Feb 6, 2007,
#5
Please don't draw a picture, that's not very accurate at all. Well, draw to set up your system, but don't just try to draw a summed vector and measure it.
#7
Wtf, I was going to answer this question as well.

Does everyone on UG take physics? lol
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#8
Well I broke it up into components and drew the picture, but all the ways I tried got the wrong answer.

I made it a single triangle with dog A on the horizontal axis, and dog B 60.2 degrees away. Tried splitting it into two triangles each with 30.1 degrees.. =/

Where I'm lost is what to do after you have the components. Cause am I just supposed to subtract/add them as if it were a regular vector equation, or does the fact that it's a rope around a pole affect the outcome?
Originally Posted by Corwinoid
Metal doesn't hold hands, it gets head in the van before the show. Seriously.


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#9
All that is is the combination of two forces.
draw the first force vector (the direction doesn't matter) of 270 N. then draw from the end of it the second force vector of 330 N at an angle of 60.2 degrees from what the first one was. conect the start with the end to get the resultant vector and use the rule of cosines to find its magnitude.
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#10
Alright, I got the right answer. Having trouble visualizing it, but I guess it's like saying rather than those 2 dogs, just have 1 dog pulling the rope w/ that vector. *shrug*

thanks guys
Originally Posted by Corwinoid
Metal doesn't hold hands, it gets head in the van before the show. Seriously.


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#12
Hehe, I like the attention to detail with the hats on the i's and j's.
#13
I know you already got it but tbh, in this situation it's probably easiest to just use trig.
#14
Quote by SaXXoN
I know you already got it but tbh, in this situation it's probably easiest to just use trig.



Yeah, you could have used the law of cosines to do this problem if you wanted.. but it's probably just best to practice breaking it into components since you'll use that a lot more than the law of cosines in physics and statics and deforms and dynamics etc. etc.
#15
Quote by Dreadnought
Wtf, I was going to answer this question as well.

Does everyone on UG take physics? lol



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#19
I have np with breaking into components, resultant vectors etc... my problem here is the concept. I dont understand why in this case you just find the resultant vector. I'm definitely overthinking it, cause it seems too simple. Clearly I'm wrong since the right answer was the resultant -_-

thanks guys
Originally Posted by Corwinoid
Metal doesn't hold hands, it gets head in the van before the show. Seriously.


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#20
Because a force is a vector quantity (like motion and velocity). That means that to add forces together, you can add their vectors. It's part of the nature of a force that you can simply find the resultant vector.
Quote by Roger_Waters
^ wow i actually almost missed that hahaha iforgot your a genious


Don't blame us if we ever doubt you, you know we couldn't live without you.

I'm oedipus, bitch, the original balla
Bust out my 9, light up your Impala
fuck that police!
#22
^ i think i saw that one in my history textbook.
Quote by Roger_Waters
^ wow i actually almost missed that hahaha iforgot your a genious


Don't blame us if we ever doubt you, you know we couldn't live without you.

I'm oedipus, bitch, the original balla
Bust out my 9, light up your Impala
fuck that police!
#23
Quote by Xinlitik
Question is killing me... I get the feeling it's really simple but I cant think about it right.

Two dogs pull horizontally on ropes attached to a post; the angle between the ropes is 60.2 degrees.

If dog A exerts a force of 270 N and dog B exerts a force of 330 N, find the magnitude of the resultant force.

Anyone know how to solve that? I dont need an answer, just the right way to look at it.

Thanks



alright, so the dogs pull on two different ropes horizontally. do they pull in opposing directio or at least different directions they have to theres an angle included at least i think there has to be... anyway on with the problem.

so basically one pulls with a force of 270 newtons and the other pulls with a force of 330 newtons. now apply trigonometry to the problem, i think. unless that only works with right triangles which i think it does. so nevermind trig. I think the law of sines or cosines has to be used. try that out. point is, you have to use some calculus function to find the resultant force (hypotenuse), im horrible with calc. so try it then since your looking for magnitude, that also requires the direction. just place the problem on the cartesian plane. 60.2 degrees from the x axis and work with it there, i think. if this makes any sense i hope it does and hope it helps
anybody wanna put anything here just let me know