How Do I Correctly Calculate the Electric Force Vector Direction and Magnitude?

[Manodesi524]

Homework Statement

http://postimage.org/image/y4h1ubp8b/

Homework Equations

F_xy=(k*q*q)/r^2

The Attempt at a Solution

This is a problem involving Electric Force:

http://postimage.org/image/y4h1ubp8b/


My goal is to find the direction and magnitude of q1. However, every time i do it, i get .04 N @ 189 degrees when our teacher says it is 262.

I am also confused about what angle i should use when finding the components on q1 and q3. Is it 64 degrees or 26 degrees? Can someone show me what angle i should use and why?

I have a big exam tommorow and i am very stressed. I'd love an answer.

The Forces are as follows: F12=.054, F13=.014, F23= .11

Here is some work: sin(26.6)*.014= .006, which is x component of vector

cos(26.6) *.014- .054=-.41, which is my y component

I do phythag to get my force, which is .41 Newtons.

When I do inverse tangent of .006/.041, i get 8 degrees. I add this to 180 to get a final answer of 188. My teacher said its near 262. What did i do??

 

[SammyS]

Homework Statement

http://postimage.org/image/y4h1ubp8b/

Homework Equations

F_xy=(k*q*q)/r^2

The Attempt at a Solution

This is a problem involving Electric Force:

http://postimage.org/image/y4h1ubp8b/


My goal is to find the direction and magnitude of q1. However, every time i do it, i get .04 N @ 189 degrees when our teacher says it is 262.

Do you mean 262 N, or 262° ?

q₁ doesn't have a direction.

Do you mean the direction of the force on q₁?

I am also confused about what angle i should use when finding the components on q1 and q3. Is it 64 degrees or 26 degrees? Can someone show me what angle i should use and why?

I have a big exam tomorrow and i am very stressed. I'd love an answer.

The Forces are as follows: F12=.054, F13=.014, F23= .11

Here is some work: sin(26.6)*.014= .006, which is x component of vector

cos(26.6) *.014- .054=-.41, which is my y component

I do phythag to get my force, which is .41 Newtons.

When I do inverse tangent of .006/.041, i get 8 degrees. I add this to 180 to get a final answer of 188. My teacher said its near 262. What did i do??

 

[VantagePoint72]

One helpful suggestion: people will be more willing to help you if you take the time to write out everything properly. Throughout your question, you've ignored units in most places (the cardinal sin of physics!), dropped zeroes (do you mean 0.41N or 0.041N?), and not explained the conventions you're using. "@ 189 degrees" doesn't mean anything to us. 189/262 degrees relative to what? And in which direction, clockwise or counter-clockwise? Like SammyS said, q1 doesn't have direction. Do you mean the force on q1? As it is, you've made it very difficult for someone to help you because you haven't taken the time the write your question out clearly. I think I've mostly been able to figure out what you mean, and I'll help you—but honestly, I'm not sure I should be doing so. I'm doing it since you have a test tomorrow, but please don't let this reinforce this kind of carelessness.

You've calculated the magnitude of the force correctly: it is indeed 0.04 Newtons (mind your significant figures!). You haven't shown which angle you're labeling with 26.6 degrees, but your components are correct (with the exception of the missing zero in your y-component). Thus, [itex]arctan(0.041N/0.006N) = 81.7^{\circ}[/itex], or the vector points 82 degrees counter-clockwise from west. If you're measuring counter-clockwise from east (as I suppose your teacher is), you get 180 degrees + 82 degrees = 262 degrees. So, it appears you just got your opposite and your adjacent components backwards.

Please put more effort into writing a clear question next time. Good luck on your test.

 

[Manodesi524]

Sorry guys! Yes I was very messy. I appreciate all of ur replies. I figured it out at about 2 last night. I'm taking honors physics in 3 weeks and it's very daunting!

 

[Nickie]

First of all, it is important to note that the problem involves electric force, which is a fundamental force in nature that acts between charged particles. The equation used to calculate electric force is given by F = k*q1*q2/r^2, where k is the Coulomb constant, q1 and q2 are the magnitudes of the charges, and r is the distance between the charges.

Based on the given diagram, it appears that q1 is the charge located at the top left corner, q2 is the charge located at the bottom left corner, and q3 is the charge located at the bottom right corner. The angles given in the diagram are the angles between the horizontal axis and the line connecting the charges.

To find the direction and magnitude of q1, we can use the equation F12 = k*q1*q2/r12^2, where r12 is the distance between q1 and q2. Similarly, F13 = k*q1*q3/r13^2 and F23 = k*q2*q3/r23^2.

To find the direction of q1, we can use the law of cosines to find the angle between q1 and q2, which is given by 180 degrees - 26.6 degrees = 153.4 degrees. Similarly, the angle between q1 and q3 is given by 180 degrees - 64.6 degrees = 115.4 degrees.

To find the x and y components of q1, we can use the trigonometric identities: cos(153.4) = -cos(26.6) and sin(153.4) = -sin(26.6). This gives us the x component as -cos(26.6)*F12 = -0.054 N and the y component as -sin(26.6)*F12 = -0.006 N.

To find the magnitude of q1, we can use the Pythagorean theorem: |q1| = sqrt((-0.054)^2 + (-0.006)^2) = 0.054 N. Therefore, the magnitude of q1 is 0.054 N and the direction is 180 degrees - 8 degrees = 172 degrees (towards the negative x-axis).

It is important to check your calculations and make sure you are using the correct equations and angles. Also, when using the inverse tangent function, make sure to use the correct signs for