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Vectors help!

  • #1
Ok Tomorrow I have a test in my physic's class and my teacher was nice enough to give us a study guide with the answers, but I can't figure out for my life how to get a few of the answers. I have 3 problems that I am having trouble with.

1. One force of 60N and a second of 30N act on an object at Point P. Graphically add the vectors and find the magnitude of the resultant when the angle between them is as follows:
a. 0
b. 30
c. 45
d. 60

Her answers: a. 90N (I got that one)
b. 87N
c. 84N
d. 79N

2. A person weighs 612N. If the person sits in the middle of a hammock that is 3.0m long and sags 1.0m below the points of support, what force would be exerted by each of the two hammock ropes?

Her answer: 457.3N

I will put the 3rd on in a little bit, just because their is a diagram that goes with it. Though I really need help with the 1st 2 b/c I just don't get one part of the 3rd question. Thanks!

Edit: since I was informed that I needed to show the troubles I having with the problems here they are:

I know in part a I just have to add the two vectors together. Then in Parts b-d I thought I was suppose to break up the vectors to have right triangles then use trig functions then Pythagorean's theorem to solve the equation.... but when ever I do that I keep on getting answers that are like 10N off. I am not sure if I am doing right. Can someone explain the steps I need to take into solving the equation.

For problem 2 ... I was wondering if someone can explain how to set up the diagram.
 
Last edited:

Answers and Replies

  • #2
Gokul43201
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keita_Otaku said:
I have 3 problems that I am having trouble with.
You must show what trouble you are having with these problems. It is against the policy to help you unless you show your work first.
 
  • #3
Gokul43201 said:
You must show what trouble you are having with these problems. It is against the policy to help you unless you show your work first.
Ok sorry.. Kind of new and didn't know that. I will get right on it. Thanks for telling me
 
  • #4
Gokul43201
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Last edited:
  • #5
Gokul43201 said:
Sure. Read this first...and welcome to PF !
I am sorry, but read what first?
 
  • #6
Gokul43201
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Oops...fixed it.
 
  • #7
Gokul43201 said:
Oops...fixed it.
I did read it, but I guess after looking at a few other people's post I just still didn't get what they were looking for. Is my 1st post right now?
 
Last edited:
  • #8
:cry: I have a feeling no one will help me because I don't understand the format of posting here.... I really need help b/c I don't get it. I have been trying for 2 hours to get these 2 questions, but of course I have an evil textbook that does not explain anything. :cry:
 
  • #9
Gokul43201
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keita : Your textbook (which one is it ?) has a pair of formulae for adding two vectors of magnitude F1 and F2 when they are separated by an angle [itex]\theta [/itex].

There's one formula telling you the magnitude of the "Resultant" vector ([itex]F^2 = F1^2 + F2^2 + 2F1F2cos \theta[/itex]). There's another one telling you the angle at which the resultant works. All these results pop out of the parallelogram approach to adding vectors. I suggest you read this part of your text.
 

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