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Dogs pulling on a post vector probelm

by kirby27
Tags: vector analysis
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kirby27
#1
Oct6-11, 06:49 PM
P: 32
Two dogs pull horizontally on ropes attached to a post; the angle between the ropes is 60.5.

If dog A exerts a force of 250 and dog B exerts a force of 330 , find the magnitude of the resultant force.

Find the the angle the resultant force makes with dog A's rope.

-I dont know where to start because i dont know what to do with the 60.5 degrees. should i split it equally between the dogs (30.25 each)? does it matter? or am i doing it wrong?
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lewando
#2
Oct6-11, 07:12 PM
PF Gold
P: 1,053
I dont know where to start because i dont know what to do with the 60.5 degrees. should i split it equally between the dogs (30.25 each)?
No, don't split the angle between the dogs.
does it matter?
Does what matter?
... or am i doing it wrong?
Doing what wrong? Please show what it is that you are doing.
kirby27
#3
Oct6-11, 07:40 PM
P: 32
ok. i know not to split the angle, but now i dont know how to get started.

lewando
#4
Oct6-11, 07:49 PM
PF Gold
P: 1,053
Dogs pulling on a post vector probelm

You realize that this is a vector addition question, yes? What methods have you used in the past? There is the graphical method with rulers and protractors, the parallelogram method if you like trig functions, to start.
kirby27
#5
Oct6-11, 09:01 PM
P: 32
i'm very good at vector adition, but i dont know how to divide these two vectors into their components. if i had angles for each vector i would understand how to do the problem
lewando
#6
Oct6-11, 09:11 PM
PF Gold
P: 1,053
Well then pick one of the dog vectors so that it aligns with the +x axis. Put the other dog vector at the angle 60.5 CW (or CCW--it does not matter) from the first dog and then add them using the component method.
kirby27
#7
Oct6-11, 09:30 PM
P: 32
ok but the question says that the dogs pull "horizontally." This means that they are both pulling on the x-axis, and their angle is created in the y-axis. isn't the wording unclear?
lewando
#8
Oct6-11, 09:35 PM
PF Gold
P: 1,053
I did not read it that way. "pulling horizontally" means that all their force is applied in a horizontal plane.
kirby27
#9
Oct6-11, 09:42 PM
P: 32
im gonna trust you on this one
lewando
#10
Oct6-11, 09:43 PM
PF Gold
P: 1,053
So, to be clear, this horizontal plane consists of an x-axis (+x pointing east, say) and a y-axis (+y pointing north). The dogs pulling horizontally means there is no z-component of force. [Edit: No short dog, tall dog scenario. ]


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