What is the correct magnitude and direction of the vector D and E?

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Homework Help Overview

The discussion revolves around the calculation of the magnitude and direction of two resultant vectors, D and E, derived from three given displacement vectors A, B, and C. Participants are using the component method to analyze their results and compare them with provided answers from a textbook.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants are attempting to calculate the resultant vectors D and E by summing the given vectors A, B, and C. They are questioning their calculations, particularly regarding discrepancies between their computed magnitudes and directions and those stated in the textbook.

Discussion Status

Several participants have shared their calculations and expressed confusion over the differences between their results and the textbook answers. There is an ongoing exploration of potential errors in the calculations, particularly in the approach to finding the direction of vector E. Some participants have suggested double-checking the given vectors and the answers provided in the book.

Contextual Notes

Participants are preparing for an upcoming test and are under pressure to understand the material correctly. There is an emphasis on ensuring that the vectors and calculations align with the problem statement, as discrepancies have been noted.

Frankie715
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Homework Statement


Consider the three displacement vectors

A=(3i-3j) m
B=(i-4j) m
C=(-2i+5j) m

Use the component method to determine (a) the magnitude and direction of the vector:

D= A+B+C and

(b) the magnitude and direction of:

E=-A-B+C

Homework Equations


The Attempt at a Solution



I did A+B+C which resulted in

2i-2j. I put them in the equation to find the magnitude which is

sqrt (2^2+(-2)^2) which resulted in 8. Square root of 8 is 2.82, but the back of the book says the answer is 4.47.

What am I doing wrong?

Thanks for any assistance!
 
Last edited:
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Well it seems good

is the answer to (b) also coming wrong?
 
Yeah,

For B) I did

arctan(-2/2) which is -45 degrees and the book says its 63.4 degrees
 
you are doing part b wrong

its not -2/2

find E again
 
cupid.callin said:
you are doing part b wrong

its not -2/2

find E again

Woops, I thought you were referring to the second part of part A to find the direction of the vector. I haven't begun part B yet. I will do it now to see if it matches the back of the book.
 
I got a magnitude of 13.4 for part B, but it is saying 8.49. What am I doing wrong?

B) -A-B+C

-6i + 12j

sqrt(36+144)=13.4
 
Anyone have any idea what I am doing wrong? I have a test on this tomorrow and would like to know how to do this (If I am doing it incorrectly).

Thanks
 
Frankie715 said:
Anyone have any idea what I am doing wrong? I have a test on this tomorrow and would like to know how to do this (If I am doing it incorrectly).

Thanks
Those answers seem right.

Double check the given vectors AND check that the answers are for this problem.
 
Dont worry,
your answers are right!Sue That book's writer! :smile:
 

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