#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

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

#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

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

#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.

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.

#6

Fu

*ck, I don't want to go into physics now .*
#7

Wtf, I was going to answer this question as well.

Does everyone on UG take physics? lol

Does everyone on UG take physics? lol

#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?

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?

#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 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.
#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

thanks guys

#11

Just do this

EDIT: whoops.. you already got it.. Well, if you need help on any other questions, let me know. It'd be a nice break from being frustrated by not knowing how to do relative motion problems.

EDIT: whoops.. you already got it.. Well, if you need help on any other questions, let me know. It'd be a nice break from being frustrated by not knowing how to do relative motion problems.

#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

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

Wtf, I was going to answer this question as well.

Does everyone on UG take physics? lol

Apparently. I was too late to help

#16

find the resultant using trig and thats it

its not hard once you get to understand it but can be awkward when you start it

its not hard once you get to understand it but can be awkward when you start it

#17

Is this your homework?

#18

^Naw its his hobby

#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

thanks guys

#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.

#22

^ i think i saw that one in my history textbook.

#23

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

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